Liquid crystal device and electronic equipment using the same

ABSTRACT

This invention refers to a liquid crystal device that provides a color display by utilizing a colorization phenomenon caused by double refraction birefringence of a liquid crystal, wherein the color tone that appears when no voltage or a non-selected voltage is applied is white or a non-color close thereto, and at least two colors are displayed when a voltage is applied, and electronic equipment in which this liquid crystal device is installed. 
     A liquid crystal device which is capable of displaying colors without using color filters and which is also capable of displaying white or a non-color close thereto is implemented by optimizing the value of Δn·d of the liquid crystal and the relationship between the value of Δn·d of the liquid crystal and the value of retardation (R) of an optically anisotropic substance such as a retardation film. 
     In other words, the liquid crystal cell and the optically anisotropic substance should be such as to satisfy the following relationships: 
     
         Δn·d≧1(μm) 
    
     
         15.5×α.sup.2 
    
      -40×α+25.1≦R-Δn·d≦15.5×.alpha. 2  -40×α+25.8(μm)

TECHNICAL FIELD

This invention relates to a liquid crystal device and electronicequipment in which a liquid crystal device is installed and, inparticular, to a liquid crystal device that provides a color display byutilizing a colorization phenomenon caused by double refractionbirefringence of the liquid crystal and electronic equipment in whichthis liquid crystal device is installed.

BACKGROUND OF ART

A prior-art color liquid crystal device that achieves a colorizeddisplay uses color filters to colorize light that is transmittedtherethrough. This color liquid crystal device is configured of a liquidcrystal display element that is formed from a liquid crystal cellprovided with a color filter and a pair of polarizing plates disposed tosandwich this liquid crystal cell, and a display drive means for drivingthe liquid crystal cell.

However, this prior-art color liquid crystal device has a problem inthat the liquid crystal display element has to use color filters tocolorize the light transmitted therethrough, so that the transmittanceof light therethrough is low and thus the display is dark.

This is caused by the absorption of light by the color filter. In otherwords, a color filter has a fairly high absorptance index for light inthe wavelength band corresponding to the color thereof, so that thequantity of colored light that has passed through this color filter isreduced in comparison with light of that wavelength band that wasincident on the color filter, and thus the display becomes darker.

Note that the liquid crystal display element in this prior-art colorliquid crystal device is of a transmittance type. If, however, areflective type of device is created by disposing a reflective plate onthe rear surface of this liquid crystal display element, light that isincident on the front surface of the liquid crystal display element, isreflected by the reflective plate on the rear surface, and is thenemitted from the front surface side passes through the color filtertwice and thus the quantity thereof is reduced so that the displaybecomes much darker and therefrom, this type is rarely used for adisplay device.

To solve the above problems, the present Applicants have previouslydeveloped a color liquid crystal device that colorizes light transmittedtherethrough without using color filters and has a high transmittance oflight, and thus is capable of providing a display of a sufficiently highluminance.

This liquid crystal device is a retardation effect color (REC) modereflective color super-twisted nematic (STN) liquid crystal device thatutilizes a method of using a colorization phenomenon created by doublerefraction birefringence of the liquid crystal, and the configurationthereof is disclosed in Japanese Patent Application Laid-Open No.2-118516.

The retardation effect color (REC) method is a method of using doublerefraction birefringence of the liquid crystal to implement a colordisplay; the retardation of the liquid crystal is varied by controllingthe voltage applied to the liquid crystal layer, so that multiple colorscan be displayed.

Since an REC mode liquid crystal device does not require any colorfilters, it is bright and also inexpensive, and is suitable for areflective liquid crystal display (LCD) in a popular type of portableelectronic equipment.

The colorization principle of an REC mode color STN to liquid crystaldevice will now be described with reference to FIG. 38.

As shown in FIG. 38, incident light (light for each of the colors red,green, blue) passes through a polarizing plate 3000 and is subjected tolinear polarization thereby, then is incident on a super-twisted nematic(STN) liquid crystal cell 3100.

Liquid crystal molecules exhibit optical anisotropy in that theirrefractive index in the long-axis direction thereof differs from therefractive index in the short-axis direction. This is called doublerefraction. This means that the speed of transmission of incidentlinearly polarized light differs in the directions of the long axis andshort axis of the liquid crystal molecules and thus the light issubjected to elliptical polarization. Since the state of this ellipticalpolarization depends on color, a difference is generated in the quantityof light of each color passing through a polarizing plate 3400, so thatlight of a predetermined color can be created by combining light ofdifferent colors that is transmitted therethrough.

If a voltage is applied to the STN liquid crystal cell 3100, theeffective value of Δn·d of the liquid crystal layer decreases as thevoltage increases. Note that Δn is the optical anisotropy of the liquidcrystal and d is the thickness of the liquid crystal layer.

Therefore, if the initial value of Δn·d could be set to be high, thevalue of Δn·d of the STN liquid crystal could be made to vary greatly bychanging the voltage applied thereto, the state of the ellipticalpolarization of light after it has passed through the liquid crystalcell is thereby varied greatly, and thus changes in display color suchas those shown in FIG. 39 can be implemented.

An REC mode color STN liquid crystal device has superior characteristicssuch as being bright and inexpensive, but further research by theinventors of the present invention has identified points that could beimproved further.

In other words, to increase the reflection luminance in a reflectivetype of liquid crystal device provided with a reflective plate on one ofthe outer sides of a polarizing plate or a transflective liquid crystaldevice provided with a transflector, it is required that the color tone(hereinafter called background color) achieved when no voltage isapplied (hereinafter referred to as "at zero voltage") or when anoff-voltage is applied should be white or a non-color close thereto,and, moreover, it is necessary that a non-color such as black or whiteis displayed as the background color even in a transmittance type ofliquid crystal device that is provided with backlighting on the outerside of a polarizing plate.

However, a liquid crystal device using the method shown in FIG. 38 tendsto have a background color that is green or blue-green, and it is knownto be difficult to always display white or a non-color close thereto.

The present invention was devised by the inventors of this applicationon the basis of the above described results of experiments.

DISCLOSURE OF INVENTION

An objective of this invention is to provide a liquid crystal devicewhich is capable of displaying at least two colors without using colorfilters and which is also capable of displaying white or a non-colorclose thereto.

Another objective thereof is to provide high-performance electronicequipment in which is installed a bright and inexpensive color displaymeans.

The liquid crystal device of this invention comprises a liquid crystalcell having a layer of nematic liquid crystal twisted to within therange of 180° to 360°, a pair of opposed polarizing plates disposed oneither side of the liquid crystal cell in a sandwich form, and anoptically anisotropic substance provided between the liquid crystal celland one polarizing plate of the pair of polarizing plates, wherein theliquid crystal cell and the optically anisotropic substance satisfy therelationships of Equations (1) and (2) below:

    Δn·d≧1(μm)                        (1)

    15.5×α.sup.2 -40×α+25.1≦R-Δn·d≦15.5×.alpha..sup.2 -40×α+25.8(μm)                    (2)

where: Δn·d is the product of the optical anisotropy Δn of the nematicliquid crystal and the thickness d of the nematic liquid crystal; and Ris the sum of the products Δnj·dj of the optical anisotropy Δnj of a jth(where j is an integer) layer of the optically anisotropic substance andthe thickness dj of the jth layer of the optically anisotropicsubstance, taken from a first layer to an ith layer (where i is aninteger greater than or equal to j) when i layers of the opticallyanisotropic substance are used. In addition, α is the ratio of theoptical anisotropy of the optically anisotropic substance at awavelength of 450 nm with respect to the optical anisotropy thereof at awavelength of 590 nm. In other words, α is Δn₄₅₀ nm /Δn₅₉₀ nm.

A liquid crystal device which is capable of displaying colors withoutusing color filters and which is also capable of displaying white or anon-color close thereto is implemented by optimizing the value of Δn·dof the liquid crystal and the relationship between the value of Δn·d ofthe liquid crystal and the value of the retardation (R) of the opticallyanisotropic substance that is, for example, a retardation film. Thisliquid crystal device has a background color that is white or anon-color close thereto, for example, and displays at least two colorswhen a voltage is applied thereto.

Note that the distinction between terms "retardation" and "Δn·d" as usedin principle in this document is such that "retardation" is used inreference to an optically anisotropic substance such as a retardationfilm, and "Δn·d" is used in reference to the liquid crystal.

When a retardation film of polyvinyl alcohol (PVA) is used as theoptically anisotropic substance, it is preferable that the liquidcrystal cell and the retardation film are configured in such a manner asto satisfy the relationship: 0.51≦R-Δn·d≦1.21(μm).

When a retardation film of polycarbonate (PC) is used as the opticallyanisotropic substance, it is preferable that the liquid crystal cell andthe retardation film are configured in such a manner as to satisfy therelationship: -0.08≦R-Δn·d≦0.62(μm).

When a retardation film of polysulfone (PSF) is used as the opticallyanisotropic substance, it is preferable that the liquid crystal cell andthe retardation film are configured in such a manner as to satisfy therelationship: -0.40≦R-Δn·d≦0.30(μm).

In a preferred embodiment, the liquid crystal device of this inventionshould have a time division drive circuit that is capable of applying atleast one other voltage between a selected voltage and a non-selectedvoltage, in addition to this selected voltage and non-selected voltage.

In another preferred embodiment, the liquid crystal cell in the liquidcrystal device of this invention should satisfy the relationship:Δn·d≧{0.8×(β-1)/(P-1)}+0.6(μm). Note that Δn·d is the product of theoptical anisotropy Δn of the nematic liquid crystal layer and thethickness d of the nematic liquid crystal layer; β is the ratio of thevoltage at which the capacitance of the liquid crystal cell is 0.3 tothe voltage at which the capacitance of the liquid crystal cell is 0.1,when the capacitance of the liquid crystal cell is 0 for a voltage of0.5 V applied between a pair of electrode substrates and the capacitanceof the liquid crystal cell is 1 for a voltage of 25 V applied betweenthe pair of electrode substrates, and P is the ratio of a selectedvoltage to a non-selected voltage.

When the above conditions are satisfied, a predetermined plurality ofcolors can be displayed by using a time division drive circuit to drivethe liquid crystal cell in a method of frame rate control.

The liquid crystal device of this invention preferably uses a polymerfilm as the optically anisotropic substance.

In addition, the polymer film that is the optically anisotropicsubstance in the liquid crystal device of this invention preferably hasa refractive index nx in the direction of the maximum refractive indexparallel to the film surface, a refractive index ny in a directionperpendicular to nx and parallel to the film surface, and a refractiveindex nz in the film thickness direction, where these refractive indicessatisfy the relationship: (nx-nz)/(nx-ny) ≦0.7.

Furthermore, the direction of the slow axis of the polymer film that isthe optically anisotropic substance of the liquid crystal device of thisinvention preferably is parallel to the film surface and also variescontinuously with respect to the film thickness direction.

In addition, a second liquid crystal cell could be used as the opticallyanisotropic substance of the liquid crystal device of this invention. Insuch a case, the value of the retardation could be varied continuously.

Furthermore, the liquid crystal used in the second liquid crystal cellof the liquid crystal device of this invention is preferably a nematicliquid crystal, and the ratio of the nematic-isotropic phase transitiontemperatures (clearing point or NI point) of the nematic liquid crystalin the second liquid crystal cell and the nematic liquid crystal used inanother liquid crystal cell is in the range of 0.8 to 1.2.

In addition, at a contacting surface between one polarizing plate of thepair of polarizing plates and the liquid crystal cell in the liquidcrystal device of this invention, the angle between the direction inwhich molecules of the nematic liquid crystal are aligned in contactwith the inner surface of the liquid crystal cell and one of theabsorption axis and polarization axis of the polarizing plate ispreferably within the range of 15° to 75°.

In addition, at a contacting surface between the liquid crystal cell andthe optically anisotropic substance in the liquid crystal device of thisinvention, the angle between the direction in which molecules of thenematic liquid crystal are aligned in contact with the inner surface ofthe liquid crystal cell and the slow axis of the optically anisotropicsubstance is preferably in the range of 60° to 120°.

In addition, at a contacting surface between the optically anisotropicsubstance and one polarizing plate of the pair of polarizing plates inthe liquid crystal device of this invention, a contacting surfacebetween the optically anisotropic substance and the polarizing plate,the angle between the slow axis of the optically anisotropic substanceand the absorption axis or polarization axis of the polarizing plate ispreferably in the range of 15° to 75°

In the liquid crystal device of this invention, one of a reflectiveplate and transflector is preferably further provided on an outer sideof one polarizing plate of the pair of polarizing plates.

Electronic equipment of this invention is provided with the abovedescribed liquid crystal device. This provides bright, inexpensive,high-performance electronic equipment.

In addition, electronic equipment of this invention is provided with theabove described liquid crystal device, and is also provided with aninput means for inputting data necessary for displaying an image on theliquid crystal device. This makes it possible to implement a compact,portable piece of electronic equipment to which data can be input, forexample.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view through an example of a liquid crystal device(a reflective type of liquid crystal device) of this invention;

FIG. 2 is a diagram illustrative of the method of recording all of themutual relationships between the directions of the absorption axes(polarization axes) of the polarizing plates, the direction the slowaxis of the retardation film, and the directions of alignment of thenematic liquid crystal in the liquid crystal device of FIG. 1;

FIG. 3A shows an example of the relationships between the directions ofthe absorption axes (polarization axes) of the polarizing plates, thedirection of the slow axis of the retardation film, and the directionsof alignment of the nematic liquid crystal in the liquid crystal deviceof FIG. 1, using the recording method of FIG. 2, and FIG. 3B showsanother example of these relationships;

FIG. 4 shows an example of ranges of the values of Δn·d of the liquidcrystal and the retardation R of the retardation film that are suitablefor achieving the desired display, when a uniaxially drawn retardationfilm of polycarbonate (PC) is used as the retardation film 2 of FIG. 1;

FIG. 5 is a CIE chromaticity diagram showing an example of the change ofcolor produced when a voltage was applied to a liquid crystal devicewithin the suitable range shown in FIG. 4;

FIG. 6 shows another example of ranges of the values of Δn·d of theliquid crystal and the retardation R of the retardation film that aresuitable for achieving the desired display, when a uniaxially drawnretardation film of polycarbonate (PC) is used as the retardation film 2of FIG. 1;

FIG. 7 is a CIE chromaticity diagram showing another example of thechange of color produced when a voltage was applied to a liquid crystaldevice within the suitable range shown in FIG. 6;

FIG. 8 shows an example of ranges of the values of Δn·d of the liquidcrystal and the retardation R of the retardation film that are suitablefor achieving the desired display, when a uniaxially drawn retardationfilm of polyvinyl alcohol (PVA) is used as the retardation film 2 ofFIG. 1;

FIG. 9 shows another example of ranges of the values of Δn·d of theliquid crystal and the retardation R of the retardation film that aresuitable for achieving the desired display, when a uniaxially drawnretardation film of polyvinyl alcohol (PVA) is used as the retardationfilm 2 of FIG. 1;

FIG. 10 shows an example of ranges of the values of Δn·d of the liquidcrystal and the retardation R of the retardation film that are suitablefor achieving the desired display, when a uniaxially drawn retardationfilm of polysulfone (PSF) is used as the retardation film 2 of FIG. 1;

FIG. 11 shows another example of ranges of the values of Δn·d of theliquid crystal and the retardation R of the retardation film that aresuitable for achieving the desired display, when a uniaxially drawnretardation film of polysulfone (PSF) is used as the retardation film 2of FIG. 1;

FIG. 12 is a sectional view through another example of the liquidcrystal device of this invention;

FIG. 13A shows an example of the mutual relationships between thedirections of the absorption axes (polarization axes) of the polarizingplates, the direction of the slow axis of the retardation film, and thedirections of alignment of the nematic liquid crystal in the liquidcrystal device of FIG. 12, and FIG. 13B shows another example of themutual relationships between these directions;

FIG. 14 is a sectional view through another example of the liquidcrystal device of this invention;

FIG. 15A shows an example of the mutual relationships between thedirections of the absorption axes (polarization axes) of the polarizingplates, the direction of the slow axis of the retardation film, and thedirections of alignment of the nematic liquid crystal in the liquidcrystal device of FIG. 14, and FIG. 15B shows another example of themutual relationships between these directions;

FIG. 16 is a sectional view through another example of the liquidcrystal device of this invention;

FIG. 17A shows an example of the mutual relationships between thedirections of the absorption axes (polarization axes) of the polarizingplates, the direction of the slow axis of the retardation film, and thedirections of alignment of the nematic liquid crystal in the liquidcrystal device of FIG. 16, and FIG. 17B shows another example of themutual relationships between these directions;

FIG. 18 is a sectional view through another example of the liquidcrystal device of this invention;

FIG. 19A shows an example of the mutual relationships between thedirections of the absorption axes (polarization axes) of the polarizingplates, the direction of the slow axis of the retardation film, and thedirections of alignment of the nematic liquid crystal in the liquidcrystal device of FIG. 18, and FIG. 19B shows another example of themutual relationships between these directions;

FIG. 20 shows the results of evaluation of the viewing anglecharacteristics of the liquid crystal device of FIG. 18;

FIG. 21 is a sectional view through another example of the liquidcrystal device of this invention;

FIG. 22A shows an example of the mutual relationships between thedirections of the absorption axes (polarization axes) of the polarizingplates, the direction of the slow axis of the retardation film, and thedirections of alignment of the nematic liquid crystal in the liquidcrystal device of FIG. 21, and FIG. 22B shows another example of themutual relationships between these directions;

FIG. 23 is a sectional view through another example of the liquidcrystal device of this invention;

FIG. 24A shows an example of the mutual relationships between thedirections of the absorption axes (polarization axes) of the polarizingplates and the directions of alignment of the nematic liquid crystal inthe liquid crystal device of FIG. 23, and FIG. 24B shows another exampleof the mutual relationships between these directions;

FIG. 25 is a diagram illustrative of the concept of the steepness ratioβ of a nematic liquid crystal;

FIG. 26 shows the relationships between Δn·d of the liquid crystal cell,the retardation R of the retardation film, and the steepness ratio P ofthe nematic liquid crystal in a liquid crystal device that satisfies therelationships within the suitable range shown in FIG. 4;

FIG. 27 is a CIE chromaticity diagram of the colors exhibited when aliquid crystal device that satisfies the relationships within thesuitable range shown in FIG. 4 is driven in eight steps;

FIG. 28 shows the relationships between on d of the liquid crystal cell,the retardation R of the retardation film, and the steepness ratio β ofthe nematic liquid crystal in a liquid crystal device that satisfies therelationships within the suitable range shown in FIG. 6;

FIG. 29 is a CIE chromaticity diagram of the colors exhibited when aliquid crystal device that satisfies the relationships within thesuitable range shown in FIG. 6 is driven in eight steps;

FIG. 30A is a diagram illustrative of the relationships between Δn·d ofthe liquid crystal cell, the retardation R of the retardation film, andthe wavelength dispersion ratio α of the retardation film, and FIG. 30Bis a diagram illustrative of the wavelength dispersion ratio α of theretardation film;

FIG. 31A is a diagram illustrative of the concept of a simulator andFIG. 31B is a graph illustrative of the general functions f₁ (α) and f₂(α);

FIG. 32 shows the exterior of an example of the electronic equipment ofthis invention (a pager) in which a liquid crystal device is installed;

FIG. 33 shows an example of a circuit for driving the liquid crystaldevice mounted in the electronic equipment of FIG. 32;

FIG. 34A shows another example of the electronic equipment of thisinvention (a controller of an air-conditioner) in which a liquid crystaldevice is installed and FIG. 34B shows yet another example of electronicequipment (a calculator);

FIG. 35 shows an example of a circuit for driving the liquid crystaldevice mounted in the electronic equipment of FIG. 34A;

FIG. 36 shows another example of the electronic equipment of thisinvention in which a liquid crystal device is installed;

FIGS. 37A to 37C are each diagrams illustrative of the function of theretardation film in the liquid crystal device of this invention;

FIG. 38 is a diagram illustrative of the principle of the color displayin an REC mode liquid crystal device; and

FIG. 39 shows an example of display colors achieved when a voltage isapplied to the liquid crystal device of FIG. 38.

BEST MODE FOR CARRYING OUT THE INVENTION

A. Conditions Necessary for Obtaining Required Results

With a liquid crystal device that uses a nematic liquid crystal(hereinafter referred to as an STN liquid crystal) that is twisted towithin the range of 180° to 360° and an optically anisotropic substanceconfigured of means such as a retardation film or a second liquidcrystal cell, to ensure that a color tone that is white or a non-colorclose thereto is displayed when a voltage applied to the STN liquidcrystal is zero and, furthermore, to ensure that at least two colors aredisplayed when voltages are applied thereto, it is necessary to satisfythe following first and second conditions:

First Condition:

    Δn·d≧1(μm)                        (1)

Second Condition:

    15.5×α.sup.2 -40×α+25.1≦R-Δn·d≦15.5×.alpha..sup.2 -40×α+25.8(μm)                    (2)

where: Δn·d is the product of the optical anisotropy Δn of the STNliquid crystal and the thickness d of the STN liquid crystal; R is thesum of the products Δnj·dj of the optical anisotropy Δnj of a jth (wherej is an integer) layer of the optically anisotropic substance and thethickness dj of the jth layer of the optically anisotropic substance,taken from a first layer to an ith layer (where i is an integer greaterthan or equal to j) when i layers of the optically anisotropic substanceare used; and α is the ratio of the optical anisotropy of the opticallyanisotropic substance at a wavelength of 450 nm with respect to theoptical anisotropy thereof at a wavelength of 590 nm.

The above first condition is necessary for causing a sufficient changein color and thus enable the display of at least two colors in apracticable manner. This first condition was deduced from the results ofvarious experiments.

The above second condition ensures that the color tone that is displayedwhen the voltage applied to the STN liquid crystal is zero is white or anon-color close thereto. This second condition was obtained bycollecting data from the results of various experiments and performingcomputer simulations on the basis of this data.

This second condition is a general equation that can be applied to allconfigurations, such as when a retardation film or a second liquidcrystal cell is used as the optically anisotropic substance, or when astack of several retardation films is used, or when retardation filmsare used above and below an STN liquid crystal cell.

B. Method of Deriving Equation for Second Condition

The above equation for the second condition was obtained by the methodshown in FIGS. 30A, 30B, 31A, and 31B.

This is described in sequence below.

First Step

Various combinations of values of Δn·d of the STN liquid crystal celland the retardation R of the optically anisotropic substance, such as aretardation film, were first combined as shown in FIG. 30A, thesesamples were investigated to determine whether or not they were capableof displaying white or a non-color, and a range thereof capable of sucha display was investigated. These experiments were performed for varioussamples with different materials and configuration to obtainexperimental data.

Functions for regulating the range in which white or a non-color can bedisplayed were then obtained for each of the experimental samples. Theresults of experiments performed by the inventors have determined thatthese functions are linear functions having a slope of 1 and having Δn·das a variable, as shown in FIG. 30A. In other words, a region in FIG.30A sandwiched between two linear functions (shown hatched in thefigure) is a range in which the display of white or a non-color can beachieved.

As shown in FIG. 30A, the two linear functions that express an upperlimit and a lower limit are R=Δn·d+b and R=Δn·d+c, where the intercepts(constants) b and c of these linear functions give upper and lowerlimiting values of the difference (R-an d) between the retardation R ofan optically anisotropic substance such as a retardation film and thevalue of Δn·d, necessary for forming the display of white or anon-color.

In other words, the display of white or a non-color is possible ifc≦R-Δn·d≦b.

However, when b and c are used as constants, it is not possible toreliably express the conditions necessary for displaying white or anon-color. That is to say, in order to express the characteristics of anoptically anisotropic substance, it is necessary to introduce awavelength dispersion ratio α. In other words, use of this wavelengthdispersion ratio a makes it possible to express the above conditionsmore accurately. This is described in detail below.

The value of the retardation R of the optically anisotropic substance isthat when the wavelength λ is 550 nm, as shown in FIG. 30B. However,although the value of the retardation R is the same throughout theoptically anisotropic substance, such as a retardation film, differentoptical anisotropies are exhibited for light at wavelengths other than550 nm. In other words, an optically anisotropic substance 900 shown inFIG. 30B exhibits a steep transition of optical anisotropy with respectto the wavelength λ, an optically anisotropic substance 920 exhibits agentle transition of optical anisotropy, and an optically anisotropicsubstance 910 exhibits an intermediate steepness in transition ofoptical anisotropy.

That is to say, each of the optically anisotropic substances 900, 910,and 920 has the same value of the retardation R, but they have differentrates of change of optical anisotropy with wavelength λ, so that itwould be possible to determine the above conditions more accurately byidentifying and expressing this characteristic of each of theseoptically anisotropic substances.

The above described difference in the rate of change of opticalanisotropy with respect to wavelength λ can be expressed by thewavelength dispersion ratio α. This wavelength dispersion ratio α is theratio of the optical anisotropy of the optically anisotropic substanceat a wavelength of 450 nm with respect to the optical anisotropy of theoptically anisotropic substance at a wavelength of 590 nm. Theintercepts b and c of the two linear functions of FIG. 30 can beexpressed more accurately by using this wavelength dispersion ratio α.

Therefore, one experimental example was obtained by determining therange in which the display of white or a non-color is enabled, as shownin FIG. 30A, and obtaining the intercepts b and c of two linearfunctions of slope 1 that define the upper and lower limits thereof.This work was repeated for each of the experimental samples.

In this manner, conditions such that F₁ (α)≦R-Δn·d≦F₂ (α) was obtainedfor each of the experimental samples. In this case, F₁ (α) and F₂ (α)are functions that represent the above intercepts b and c, using thewavelength dispersion ratio α as a parameter.

If a retardation film formed of polyvinyl alcohol (PVA) is used as theoptically anisotropic substance, the results of experiments havedetermined that a display of white or a non-color is enabled when theliquid crystal cell and the retardation film satisfy the followingrelationship:

    0.51≦R-Δn·d≦1.21(μm).

In addition, if a retardation film formed of polycarbonate (PC) is usedas the optically anisotropic substance, it has been determined that adisplay of white or a non-color is enabled when the liquid crystal celland the retardation film satisfy the following relationship:

    -0.08≦R-Δn·d≦0.62(μm)

Furthermore, if a retardation film formed of polysulfone (PSF) is usedas the optically anisotropic substance, it has been determined that adisplay of white or a non-color is enabled when the liquid crystal celland the retardation film satisfy the following relationship:

    -0.40<R-Δn·d<0.30(μm).

Second Step

The above first step obtained data relating to a suitable display rangeon the basis of the results of experiments. This second step performedcomputer simulations within ranges that were not derived experimentallyin the first step, to obtain data relating to a suitable display range,similar to that of the first step. The data obtained by the first stepand the data obtained by this computer simulation were comprehensivelyanalyzed, and equations were derived therefrom to determine generalizedconditions, irrespective of the material or arrangement of the opticallyanisotropic substance or the configuration of the liquid crystal cell.Finally, specific embodiments of the thus derived condition equationswere implemented by computer simulation to verify the presence of arange in which the display of white or a non-color is enabled. Thus wereobtained condition equations.

In other words, the condition f₁ (α)≦R-Δn·d≦f₂ (α) was obtained, asshown in FIG. 31B. In this case, each of f₁ (α) and f₂ (α) is ageneralized function of the value of the retardation R which enables thedisplay of white or a non-color, with the wavelength dispersion ratio αexpressed as a parameter.

More specifically, f₁ (α) and f₂ (α) can be expressed as follows:

    f.sub.1 (α)=15.5×α.sup.2 -40×α+25.1(units are μm)

    f.sub.2 (α)=15.5×α.sup.2 -40×α+25.8 (units are μm)

The above described second condition was obtained therefrom.

The simulation is described in detail below.

This simulation was performed by a simulator 100 as shown in FIG. 31A.This simulator 100 has a matrix calculation means 110 acting as afunctional block, and polarization characteristics of ellipticallypolarized light after passing through the optically anisotropicsubstance are analyzed by this matrix calculation means 100.

The description now turns to the principle of calculating the changes inthe state of polarization of the light that has passed through theliquid crystal cell and the optically anisotropic substance such as aretardation film.

Light that is incident on the optically anisotropic substance isgenerally subjected to elliptical polarization, and the reference traceof the elliptically polarized light in the positive Z-axis direction canbe expressed as in the column vector of Equation a, using the xycomponents as elements; ##EQU1## where: ai is the amplitude of an ithcomponent, ω is angular frequency, and φi is the phase angle of the ithcomponent. Since the absolute phase of the wave motion causes noproblems in this case, the optical frequency and absolute phase itemscan be omitted, and thus the polarization state is expressed by anormalized Jones' vector in which the amplitude of each component isstandardized, as shown by Equation b: ##EQU2##

The state of polarization of light that has passed through an opticallyanisotropic substance changes, so the polarized light E of Equation bbecomes polarized light E'. An optically anisotropic substance can beexpressed as a 2×2 matrix that performs this transform.

If, for example, this optically anisotropic substance is a uniaxiallinear phase element, the Jones' matrix R (Δ, θ) thereof can beexpressed by Equation c: ##EQU3## where: θ is the angle between the fastaxis of the linear phase element and the X axis, Δ is defined by thevalue of Δn·d of the linear phase element and the wavelength λ of thelight, such that Δ≡2×π×(Δn·d)/λ.

The state of polarization of light that has passed through this linearphase element is obtained from Equation d, by applying the Jones' matrixR (Δ, θ) of Equation c:

Equation d

    E'=R(Δ, θ)E

In addition, if the optically anisotropic substance is a plurality ofsuperimposed uniaxial linear phase elements, this polarization state isobtained from Equation e, by applying the Jones' matrix of Equation Csequentially:

Equation e

    E'=R(Δ.sub.n, θ.sub.n)R(Δ.sub.n-1, θ.sub.n-1) . . . R(Δ.sub.2, θ.sub.2)R(Δ.sub.1, θ.sub.1)E

If the optically anisotropic substance is a liquid crystal cell in whichthe molecules of liquid crystal are twisted, calculation of the state ofthe polarization is complicated. However, if the liquid crystal layer isdivided into a sufficiently large number of layers, it can beapproximated by adding the products of liquid crystal layers with notwist orientation. Since a liquid crystal layer with no twist is auniaxial linear polarization element, a plurality of such layers can besuperimposed in a manner similar to that of the previously describeduniaxial linear polarization elements to make it possible to obtain thestate of polarization of light that has passed through the liquidcrystal cell.

The polarization state were obtained by applying suitable parameters inthe above method.

It was thus verified that satisfaction of the above first and secondconditions ensures that the color tone at zero voltage is white or anon-color close thereto and color changes to at least two colors aredisplayed when a voltage is applied, even when polycarbonate, polyvinylalcohol, polysulfone or various types of second liquid crystal cell areused as the optically anisotropic substance.

C. Characteristics of the Liquid crystal device of this Invention

The characteristics of the liquid crystal device of this invention willnow be described briefly below, with reference to FIGS. 37A, 37B, and37C.

The liquid crystal device of this invention is configured of thepreviously described REC mode color liquid crystal device of FIG. 38, towhich is further added an optically anisotropic substance 3200 such as aretardation film formed of a uniaxial polymer film and which can be madeto display white or a non-color by phase compensation of light by thisoptically anisotropic substance 3200.

In other words, elliptically polarized light that has passed through theliquid crystal cell 3100 is converted in reverse by the opticalcompensation effect of the optically anisotropic substance 3200 such asa retardation film, so that the display of white is enabled by returningthe polarization to substantially the same linear polarization of theincident light, as shown in FIG. 37A.

In addition, a state in which light is completely blocked (a blackdisplay) can be achieved by ensuring that the direction of linearlypolarized light that has passed through the optically anisotropicsubstance 3200 is perpendicular to the polarization axis of thepolarizing plate 3400, as shown in FIG. 37B.

Furthermore, the display of at least two colors is enabled by applying avoltage to change the optical refractive index of the liquid crystalcell 3100 and thus changing the polarization state of each of red,green, and blue light after it has passed through the opticallyanisotropic substance 3200, as shown in FIG. 37C.

This invention is described more specifically below, with the aid ofembodiments thereof.

EMBODIMENT 1

This embodiment gives examples of the use of a single uniaxially drawnretardation film as the optically anisotropic substance.

A sectional view through a reflective type of liquid crystal device isshown in FIG. 1.

This reflective type of liquid crystal device is configured to comprisean upper polarizing plate 1, a retardation film 2, a liquid crystal cell3, a lower polarizing plate 4, and a reflective plate 5.

The liquid crystal cell 3 is formed of a layer of nematic liquid crystal10 sandwiched between an upper substrate 7 having electrodes 6 on alower surface thereof and a lower substrate 9 having electrodes 8 on anupper surface thereof.

The nematic liquid crystal 10 is given a twist orientation byimplementing a process such as rubbing on alignment layers 11 and 12formed on the upper and lower substrates 7 and 9.

A sealing material 13 disposed in a peripheral portion between the upperand lower substrates 7 and 9 holds the nematic liquid crystal 10 betweenthe upper and lower substrates 7 and 9 and also keeps the distancebetween the upper and lower substrates 7 and 9 constant. In addition,spacers 14 that are glass fibers, plastic balls, or the like may bearranged between the upper and lower substrates 7 and 9. A drive circuit15 capable of applying at least three voltages is connected between theupper and lower electrodes 6 and 8. A preferable example of this drivecircuit is a time division drive circuit provided with a function ofdisplaying gray scale by frame rate control or pulse width modulation.

With the above reflective type of liquid crystal device, display is bylight (natural light or light from an illuminating light source) that isincident on the front surface side thereof being reflected by thereflective plate 5 on the rear surface side, the incident light from thefront surface side passes through the upper polarizing plate 1, theretardation film 2, STN liquid crystal 10, and the lower polarizingplate 4 before being reflected by the reflective plate 5, then passesagain through the lower polarizing plate 4, the STN liquid crystal 10,the retardation film 2, and the upper polarizing plate 1 and is emitted.

In the liquid crystal cell 3, linearly polarized light that has passedthrough the upper polarizing plate 1 and is incident thereon issubjected to the polarization action of the retardation film 2 as itpasses through the retardation film 2 and is thus ellipticallypolarized, then it is subjected to the further polarization action ofthe STN liquid crystal 10 as it passes through the STN liquid crystal10, so that the polarization state thereof is changed.

Therefore, light that has passed through the retardation film 2 and theSTN liquid crystal 10 and is incident on the lower polarizing plate 4has been subjected to the polarization actions of the retardation film 2and the STN liquid crystal 10 and is thereby polarized in a non-linearmanner; of this non-linearly polarized light, only light of thewavelength of the polarized component that passes through the lowerpolarizing plate 4 does pass through the lower polarizing plate 4 andbecome colorizing light.

In this case, the polarization action of the retardation film 2 does notvary but the orientation state of the liquid crystal molecules in theSTN liquid crystal 10 does vary in accordance with the voltage appliedbetween the electrodes 6 and 8 so that the STN liquid crystal 10 has apolarization action that changes with the orientation state of theliquid crystal molecules in the STN liquid crystal 10.

The description below concerns the colorization of light transmittedthrough the retardation film 2, caused by the polarization actionthereof. Light from the exterior is subjected to linear polarization bythe upper polarizing plate 1, is incident on the retardation film 2which has a slow axis that is at a predetermined angle with respect tothe polarization axis of the upper polarizing plate 1, and is subjectedto a polarization action corresponding to the retardation R of theretardation film 2 as it passes through this retardation film 2, thusbecoming elliptically polarized.

If elliptically polarized light emitted from the retardation film 2subsequently passes unchanged through the STN liquid crystal 10 and isincident on the lower polarizing plate 4, only light of the wavelengthof the polarized component of this elliptically polarized light thatpasses through the lower polarizing plate 4 does pass through the lowerpolarizing plate 4, so that the light that has passed through the lowerpolarizing plate 4 (linearly polarized light) becomes colorizing light.

The colorizing light that has passed through the lower polarizing plate4 is then reflected by the reflective plate 5, returns along a path thatis the reverse of the optical path described above, and is emitted fromthe upper polarizing plate 1, and a display pattern is produced by thiscolorizing light.

Note that, in this case, the colorizing light reflected by thereflective plate 5 is only light of the wavelength of the polarizedcomponent that has passed through the lower polarizing plate 4, of thelight that was polarized in a non-linear manner by the above describedpolarization actions of the retardation film 2 and the STN liquidcrystal 10, and this light is again subjected to the polarizationactions of the STN liquid crystal 10 and the retardation film 2 so thatthe colorizing light that passes through and is emitted from the upperpolarizing plate 1 is light of an even better color purity thancolorizing light reflected by the reflective plate 5.

In this manner, this reflective type of liquid crystal device colorizeslight that is transmitted therethrough without using color filters, andthus the transmittance of light therethrough is good and it can providea luminance of display that is sufficiently high.

The mutual relationships between the directions of the absorption axes(or polarization axes) of the polarizing plates 1 and 4 of FIG. 1, thedirection of the slow axis of the retardation film 2, and the directionin which the nematic liquid crystal 10 is aligned are shown in FIGS. 3Aand 3B. FIGS. 3A and 3B are differentiated by the direction of theabsorption axis (or polarization axis) of the upper polarizing plate 1.

The relationships between the situation of FIG. 3A and the configurationof FIG. 1 are shown in FIG. 2.

As shown in FIG. 2, the STN liquid crystal layer 10 is provided withliquid crystal molecules 50 that are twisted, the optical anisotropy ofthese liquid crystal molecules 50 is Δn, and the thickness of the liquidcrystal layer is d. The retardation R of the retardation film 2 isexpressed by the product (Δn1·d1) of the optical anisotropy Δn·d of theretardation film 2 and the thickness d1 of the retardation film 2.

Note that, although rubbing was used as the method of orientating thenematic liquid crystal 10 in this embodiment, another method such asoblique evaporation of SiO could be used. In the description below, thedirections in which the nematic liquid crystal 10 in contact with theupper and lower substrates 7 and 9 are orientated are called thedirections of rubbing of the upper and lower planes.

In FIGS. 3A and 3B, A1 and A2 are the directions of the absorption axes(or polarization axes) of the upper and lower polarizing plates 1 and 4,B1 is the direction of the slow axis of the retardation film 2, and C1and C2 are the directions of rubbing of the upper and lower planes.

In addition, T is the twist angle of the nematic liquid crystal 10, θ1is the angle between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2, θ2 is the angle between thedirection B1 of the slow axis of the retardation film 2 and thedirection of rubbing C1 of the upper plane, and θ3 is the angle betweenthe direction of rubbing C2 of the lower plane and the direction A2 ofthe absorption axis (or polarization axis) of the lower polarizing plate4.

θ1 is set to be more than 0° and less than 90°. With the aboveconfiguration, the opposing arrangement of the upper and lowersubstrates 7 and 9 is such that the twist angle T of the nematic liquidcrystal 10 is in the range of 180° to 360°. In this case, the twistangle T of the nematic liquid crystal 10 is governed by the directionsof rubbing C1 and C2 of the upper and lower planes and the type andquantity of substance having an optical rotatory power added to thenematic liquid crystal 10.

Embodiment 1-1

A uniaxially drawn film of polycarbonate (hereinafter abbreviated to PC)was used as the retardation film 2 in the above described theconfiguration of FIGS. 1 and 3A. In this case, the ratio α of theoptical anisotropy at a wavelength of 450 nm with respect to the opticalanisotropy at a wavelength of 590 nm (i.e., the wavelength dispersion)was 1.09.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 was set to 35° to 55°, theangle θ2 between the direction B1 of the slow axis of the retardationfilm 2 and the direction of rubbing C1 of the upper plane was set to 80°to 100°, the angle θ3 between the direction of rubbing C2 of the lowerplane and the direction A2 of the absorption axis (or polarization axis)of the lower polarizing plate 4 was set to 35° to 55°, variouscombinations of the product Δn·d of the optical anisotropy Δn and thethickness d of the nematic liquid crystal 10 and the product Δn1·d1 ofthe optical anisotropy Δn1 and the thickness d1 of the retardation film2 (hereinafter referred to as the retardation R for Embodiment 1) wereset up as shown in Table 1 below, and the change of color produced whena voltage was applied between the upper and lower electrodes 6 and 8 wasmeasured with a spectrophotometer (IMUC-7000, manufactured by OtsukaElectronics.

                  TABLE 1                                                         ______________________________________                                        No.      Δn                                                                             d (μm)  Δn · d (μm)                                                         R (μm)                                  ______________________________________                                        1        0.13   7.0        0.91    1.4                                        2        0.18   7.0        1.26    1.8                                        3        0.18   7.0        1.26    2.0                                        4        0.18   7.0        1.26    2.2                                        5        0.23   7.0        1.61    1.8                                        6        0.23   7.0        1.61    2.0                                        7        0.23   7.0        1.61    2.2                                        8        0.24   8.0        1.92    1.8                                        9        0.24   8.0        1.92    2.0                                        10       0.24   8.0        1.92    2.2                                        ______________________________________                                    

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and at least two colors are displayed when avoltage was applied, provided that the retardation R of the retardationfilm 2 and the product Δn·d of the optical anisotropy Δn and thethickness d of the nematic liquid crystal 10 were in a predeterminedrelationship. These results are shown in FIG. 4.

In FIG. 4, a portion (a) is a range within which the color tone at zerovoltage is white or a non-color close thereto and at least two colorsare displayed when a voltage is applied. In other words, this is theregion in which the previously described first and second conditions aresatisfied.

Therefore, within the range (a) in FIG. 4, the color tone at zerovoltage is white or a non-color close thereto and at least two colorsare displayed when a voltage is applied.

Conversely, outside the range (a) of FIG. 4, either the color tone atzero voltage was not white or a non-color close thereto, or display ofat least two colors did not occur when a voltage was applied.

To demonstrate an example of conditions within the portion (a) of FIG.4, FIG. 5 shows color changes with respect to applied voltage thatoccurred when a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.23 and thethickness d was 7 μm, in other words in which Δn·d was 1.61 μm, and theretardation R of the retardation film 2 was 2 μm.

In this example, the color tone at zero voltage was a bluish white, atan effective voltage of 2.15 V it was orange, at 2.20 V it was blue, andat 2.22 V it was green. In other words, this example exhibits one of themost suitable sets of conditions for the liquid crystal device of thisinvention.

In addition, to demonstrate conditions that show the region that is aboundary at which the color tone at zero voltage becomes white or anon-color close thereto within the portion (a) of FIG. 4, a liquidcrystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the retardation R of theretardation film 2 was 2.2 μm, alternatively a liquid crystal cell 3 wasused in which the optical anisotropy Δn of the nematic liquid crystal 10was 0.18 and the thickness d was 7 μm, in other words in which Δn·d was1.26 μm, and the retardation R of the retardation film 2 was 1.8 μm; inthese cases, the color tone at zero voltage was a reddish white. When avoltage was applied, color changes to orange, blue, and green occurredas the voltage increased. In other words, these are boundary conditionsfor the liquid crystal device of this invention.

Conversely, to demonstrate conditions outside the portion (a) of FIG. 4under which the color tone at zero voltage is not white or a non-colorclose thereto, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.18 and thethickness d was 7 μm, in other words in which Δn·d was 1.26 μm, and theretardation R of the retardation film 2 was 2 μm, alternatively a liquidcrystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.24 and the thickness d was 8 μm, inother words in which Δn·d was 1.92 μm, and the retardation R of theretardation film 2 was 2 μm; and the color tone at zero voltage wasorange in the former case, and in the latter case, the color tone atzero voltage was a bluish black. In other words, these are conditionsthat are not suitable for the liquid crystal device of this invention.

To further demonstrate conditions outside the portion (a) of FIG. 4under which display of at least two colors does not occur when a voltageis applied although the color tone displayed at zero voltage is white ora non-color close thereto, a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.13 and thethickness d was 7 μm, in other words in which Δn·d was 0.91 μm, and theretardation R of the retardation film 2 was 1.4 μm; in this case, thecolor tone at zero voltage was a bluish white, but the color changedonly to orange when a voltage was applied. In other words, these areconditions that are not suitable for the liquid crystal device of thisinvention.

Embodiment 1-2

A uniaxially drawn film of PC was used as the retardation film 2 in theconfiguration of FIGS. 1 and 3B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 was set to 35° to 55°, theangle θ2 between the direction B1 of the slow axis of the retardationfilm 2 and the direction of rubbing C1 of the upper plane was set to 80°to 100°, the angle θ3 between the direction of rubbing C2 of the lowerplane and the direction A2 of the absorption axis (or polarization axis)of the lower polarizing plate 4 was set to 35° to 55°, combinations ofthe product Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10 and the retardation R of the retardation film2 were set up as shown in Table 2 below, and the change of colorproduced when a voltage was applied between the upper and lowerelectrodes 6 and 8 was measured with a spectrophotometer.

                  TABLE 2                                                         ______________________________________                                        No.      Δn                                                                             d (μm)  Δn · d (μm)                                                         R (μm)                                  ______________________________________                                        1        0.13   7.0        0.91    1.2                                        2        0.18   7.0        1.26    1.4                                        3        0.20   7.0        1.4     1.6                                        4        0.20   7.0        1.4     1.8                                        5        0.20   7.0        1.4     2.0                                        6        0.23   7.0        1.61    1.6                                        7        0.23   7.0        1.61    1.8                                        8        0.23   7.0        1.61    2.0                                        9        0.24   8.0        1.92    1.6                                        10       0.24   8.0        1.92    1.8                                        11       0.24   8.0        1.92    2.0                                        ______________________________________                                    

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and at least two colors were displayed when avoltage was applied, provided that the retardation R of the retardationfilm 2 and the product Δn·d of the optical anisotropy Δn and thethickness d of the nematic liquid crystal 10 were in a predeterminedrelationship. These results are shown in FIG. 6.

In FIG. 6, a portion (a) is a range within which the color tone at zerovoltage is white or a non-color close thereto and at least two colorsare displayed when a voltage is applied, so that this is the range inwhich the previously described first and second conditions aresatisfied.

Therefore, within the range included in the portion (a) of FIG. 6, thecolor tone at zero voltage was white or a non-color close thereto and atleast two colors are displayed when a voltage was applied.

Conversely, in the range that is not within the portion (a) of FIG. 6,either the color tone at zero voltage was not white or a non-color closethereto, or display of at least two colors did not occur when a voltagewas applied.

To demonstrate an example of conditions within the portion (a) of FIG.6, a curve (a) of FIG. 7 shows color changes with respect to appliedvoltage that occurred when a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.23 and thethickness d was 7 μm, in other words in which Δn·d was 1.61 μm, and theretardation R of the retardation film 2 was 1.8 μm. The color tone atzero voltage was a yellowish white, at an effective voltage of 2.20 V itwas black, at 2.23 V it was blue, at 2.25 V it was a yellow-green, andat 2.35 V it was pink. In other words, this is one set of conditionsthat is most suitable for the liquid crystal device of this invention.

In addition, to demonstrate the boundary conditions at which it isassumed the color tone at zero voltage becomes white or a non-colorclose thereto within the portion (a) of FIG. 6, a liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the retardation film 2was 2 μm, alternatively a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.2 and thethickness d was 7 μm, in other words in which Δn·d was 1.4 μm, and theretardation R of the retardation film 2 was 1.8 μm; in these cases, thecolor tone at zero voltage was gray dark. When a voltage was applied,color changes to black, blue, yellow-green, and pink occurred as thevoltage increased. In other words, these are boundary conditions for theliquid crystal device of this invention.

Furthermore, as an example of another set of conditions within theportion (a) of FIG. 6, a curve (b) in FIG. 7 shows color changes withrespect to applied voltage that occurred when a liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.18 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.26 μm, and the retardation R of the retardation film 2was 1.4 μm. The color tone at zero voltage was a greenish white, at aneffective voltage of 2.18 V it was orange, at 2.22 V it was blue, and at2.25 V it was green.

In other words, this is one set of conditions that is most suitable forthe liquid crystal device of this invention. In addition, when a liquidcrystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.22 and the thickness d was 7 μm, inother words in which Δn·d was 1.54 μm, and the retardation R of theretardation film 2 was 1.7 μm, substantially the same color changes asthose of curve (b) in FIG. 7 occurred; when Δn·d was 1.6 μm or less, bymodulating the angle θ1 between the direction A1 of the absorption axis(or polarization axis) of the upper polarizing plate 1 and the directionB1 of the slow axis of the retardation film 2, the angle θ2 between thedirection B1 of the slow axis of the retardation film 2 and thedirection of rubbing C1 of the upper plane, and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4,color changes similar to those of curve (a) of FIG. 7 became colorchanges similar to those of curve (b) of FIG. 7.

Conversely, to demonstrate conditions outside the portion (a) of FIG. 6under which the color tone at zero voltage is not white or a non-colorclose thereto, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.2 and the thicknessd was 7 μm, in other words in which Δn·d was 1.4 μm, and the retardationR of the retardation film 2 was 2 μm, alternatively a liquid crystalcell 3 was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.24 and the thickness d was 8 μm, in other words inwhich Δn·d was 1.92 μm, and the retardation R of the retardation film 2was 1.8 μm; the color tone at zero voltage was black in the former caseand the color tone at zero voltage was yellow in the latter case. Inother words, these are conditions that are not suitable for the liquidcrystal device of this invention.

To further demonstrate conditions outside the portion (a) of FIG. 6under which display of at least two colors does not occur when a voltageis applied although the color tone displayed at zero voltage is white ora non-color close thereto, a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.13 and thethickness d was 7 μm, in other words in which Δn·d was 0.91 μm, and theretardation R of the retardation film 2 was 1.2 μm; in this case, thecolor tone at zero voltage was a yellowish white, but the color changedonly to orange when a voltage was applied. In other words, theseconditions are undesirable for the liquid crystal device of thisinvention.

Embodiment 1-3

A uniaxially drawn film of polyvinyl alcohol (hereinafter abbreviated toPVA) was used as the retardation film 2 in the above describedconfiguration of FIGS. 1 and 3A.

In this case, the ratio α of the optical anisotropy at a wavelength of450 nm with respect to the optical anisotropy at a wavelength of 590 nmwas 1.01. In addition, the twist angle T of the nematic liquid crystal10 was set to 240°, the angle θ1 between the direction A1 of theabsorption axis (or polarization axis) of the upper polarizing plate 1and the direction B1 of the slow axis of the retardation film 2 was setto 35° to 55°, the angle θ2 between the direction B1 of the slow axis ofthe retardation film 2 and the direction of rubbing C1 of the upperplane was set to 80° to 100°, the angle θ3 between the direction ofrubbing C2 of the lower plane and the direction A2 of the absorptionaxis (or polarization axis) of the lower polarizing plate 4 was set to35° to 55°, combinations of the product Δn·d of the optical anisotropyΔn and the thickness d of the nematic liquid crystal 10 and theretardation R of the retardation film 2 were set up as shown in Table 3,and the change of color produced when a voltage was applied between theupper and lower electrodes 6 and 8 was measured with aspectrophotometer.

                  TABLE 3                                                         ______________________________________                                        No.      Δn                                                                             d (μm)  Δn · d (μm)                                                         R (μm)                                  ______________________________________                                        1        0.13   7.0        0.91    2.0                                        2        0.18   7.0        1.26    2.4                                        3        0.18   7.0        1.26    2.6                                        4        0.18   7.0        1.26    2.8                                        5        0.23   7.0        1.61    2.4                                        6        0.23   7.0        1.61    2.6                                        7        0.23   7.0        1.61    2.8                                        8        0.24   8.0        1.92    2.4                                        9        0.24   8.0        1.92    2.6                                        10       0.24   8.0        1.92    2.8                                        ______________________________________                                    

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and at least two colors were displayed when avoltage was applied, provided that the retardation R of the retardationfilm 2 and the product Δn·d of the optical anisotropy Δn and thethickness d of the nematic liquid crystal 10 were in a predeterminedrelationship. These results are shown in FIG. 8.

In FIG. 8, a portion (a) is a range within which the color tone at zerovoltage is white or a non-color close thereto and at least two colorsare displayed when a voltage is applied, so that this is the range inwhich both of the previously described first and second conditions aresatisfied.

Therefore, within the range (a) of FIG. 8, the color tone at zerovoltage was white or a non-color close thereto and at least two colorswere displayed when a voltage was applied. Conversely, outside the range(a) of FIG. 8, either the color tone at zero voltage was not white or anon-color close thereto, or display of at least two colors did not occurwhen a voltage was applied.

To demonstrate an example of conditions within the portion (a) of FIG.8, a liquid crystal cell 3 was used in which the optical anisotropy Δnof the nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm,in other words in which Δn·d was 1.61 μm, and the retardation R of theretardation film 2 was 2.6 μm. In this example, the color tone at zerovoltage was a yellowish white, at an effective voltage of 2.12 V it wasorange, at 2.17 V it was blue, and at 2.19 V it was green. In otherwords, this is one set of conditions that is most suitable for theliquid crystal device of this invention.

In addition, to demonstrate the boundary conditions at which it isassumed the color tone at zero voltage becomes white or a non-colorclose thereto within the portion (a) of FIG. 8, a liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the retardation film 2was 2.8 μm, alternatively a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.18 and thethickness d was 7 μm, in other words in which Δn·d was 1.26 μm, and theretardation R of the retardation film 2 was 2.4 μm. In these examples,the color tone at zero voltage was a reddish white. When a voltage wasapplied, color changes to orange, blue, and green occurred as thevoltage increased. In other words, these are boundary conditions for theliquid crystal device of this invention.

Conversely, to demonstrate conditions outside the portion (a) of FIG. 8under which the color tone at zero voltage is not white or a non-colorclose thereto, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.18 and thethickness d was 7 μm, in other words in which Δn·d was 1.26 μm, and theretardation R of the retardation film 2 was 2.6 μm, alternatively aliquid crystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.24 and the thickness d was 8 μm, inother words in which Δn·d was 1.92 μm, and the retardation R of theretardation film 2 was 2.6 μm; in the former case, the color tone atzero voltage was orange, and in the latter case, the color tone at zerovoltage was blue. In other words, these are conditions that are notsuitable for the liquid crystal device of this invention.

To further demonstrate conditions outside the portion (a) of FIG. 8under which display of at least two colors does not occur when a voltageis applied although the color tone displayed at zero voltage is white ora non-color close thereto, a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.13 and thethickness d was 7 μm, in other words in which Δn·d was 0.91 μm, and theretardation R of the retardation film 2 was 2 μm; in this case, thecolor tone at zero voltage was a bluish white, but the color changedonly to orange when a voltage was applied. In other words, these areconditions that are not suitable for the liquid crystal device of thisinvention.

Embodiment 1-4

A uniaxially drawn film of PVA was used as the retardation film 2 in theconfiguration of FIGS. 1 and 3B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 was set to 35° to 55°, theangle θ2 between the direction B1 of the slow axis of the retardationfilm 2 and the direction of rubbing C1 of the upper plane was set to 80°to 100°, the angle θ3 between the direction of rubbing C2 of the lowerplane and the direction A2 of the absorption axis (or polarization axis)of the lower polarizing plate 4 was set to 35° to 55°, combinations ofthe product Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10 and the retardation R of the retardation film2 were set up as shown in Table 4, the change of color produced when avoltage was applied between the upper and lower electrodes 6 and 8 wasmeasured with a spectrophotometer.

                  TABLE 4                                                         ______________________________________                                        No.      Δn                                                                             d (μm)  Δn · d (μm)                                                         R (μm)                                  ______________________________________                                        1        0.13   7.0        0.91    1.8                                        2        0.18   7.0        1.26    2.0                                        3        0.20   7.0        1.4     2.2                                        4        0.20   7.0        1.4     2.4                                        5        0.20   7.0        1.4     2.6                                        6        0.23   7.0        1.61    2.2                                        7        0.23   7.0        1.61    2.4                                        8        0.23   7.0        1.61    2.6                                        9        0.24   8.0        1.92    2.2                                        10       0.24   8.0        1.92    2.4                                        11       0.24   8.0        1.92    2.6                                        ______________________________________                                    

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and at least two colors were displayed when avoltage was applied, provided that the retardation R of the retardationfilm 2 and the product Δn·d of the optical anisotropy Δn and thethickness d of the nematic liquid crystal 10 were in a predeterminedrelationship. These results are shown in FIG. 9.

In FIG. 9, a portion (a) is a range within which the color tone at zerovoltage is white or a non-color close thereto and at least two colorsare displayed when a voltage is applied, so that this is the range inwhich both of the previously described first and second conditions aresatisfied.

Therefore, within the range (a) of FIG. 9, the color tone at zerovoltage was white or a non-color close thereto and at least two colorswere displayed when a voltage was applied. Conversely, outside the range(a) of FIG. 9, either the color tone at zero voltage was not white or anon-color close thereto, or display of at least two colors did not occurwhen a voltage was applied.

To demonstrate an example of conditions within the portion (a) of FIG.9, a liquid crystal cell 3 was used in which the optical anisotropy Δnof the nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm,in other words in which Δn·d was 1.61 μm, and the retardation R of theretardation film 2 was 2.4 μm. In this example, the color tone at zerovoltage was a yellowish white, at an effective voltage of 2.24 V it wasblack, at 2.27 V it was blue, at 2.29 V it was a yellow-green, and at2.39 V it was pink. In other words, this is one set of conditions thatis most suitable for the liquid crystal device of this invention.

In addition, to demonstrate the boundary conditions at which it isassumed the color tone at zero voltage becomes white or a non-colorclose thereto within the portion (a), a liquid crystal cell 3 was usedin which the optical anisotropy Δn of the nematic liquid crystal 10 was0.23 and the thickness d was 7 μm, in other words in which Δn·d was 1.61μm, and the retardation R of the retardation film 2 was 2.6 μm,alternatively a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.2 and the thicknessd was 7 μm, in other words in which Δn·d was 1.4 μm, and the retardationR of the retardation film 2 was 2.4 μm; in this case, the color tone atzero voltage was gray. When a voltage was applied, color changes toblack, blue, yellow-green, and pink occurred as the voltage increased.In other words, these are boundary conditions for the liquid crystaldevice of this invention.

Furthermore, as an example of another set of conditions within the range(a) of FIG. 9, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.18 and thethickness d was 7 μm, in other words in which Δn·d was 1.26 μm, and theretardation R of the retardation film 2 was 2 μm. In this example, thecolor tone at zero voltage was a greenish white, at an effective voltageof 2.21 V it was orange, at 2.25 V it was blue, and at 2.28 V it wasgreen. In other words, this is one set of conditions that is mostsuitable for the liquid crystal device of this invention.

Conversely, to demonstrate conditions outside the range (a) of FIG. 9under which the color tone at zero voltage is not white or a non-colorclose thereto, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.2 and the thicknessd was 7 μm, in other words in which Δn·d was 1.4 μm, and the retardationR of the retardation film 2 was 2.6 μm, alternatively a liquid crystalcell 3 was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.24 and the thickness d was 8 μm, in other words inwhich Δn·d was 1.92 μm, and the retardation R of the retardation film 2was 2.2 μm; the color tone at zero voltage was black in the former caseand the color tone at zero voltage was yellow in the latter case. Inother words, these are conditions that are not suitable for the liquidcrystal device of this invention.

To further demonstrate conditions outside the range (a) of FIG. 9 underwhich display of at least two colors does not occur when a voltage isapplied although the color tone displayed at zero voltage is white or anon-color close thereto, a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.13 and thethickness d was 7 μm, in other words in which Δn·d was 0.91 μm, and theretardation R of the retardation film 2 was 1.8 μm; in this case, thecolor tone at zero voltage was a yellowish white, but the color changedonly to orange when a voltage was applied. In other words, these areconditions that are not suitable for the liquid crystal device of thisinvention.

Embodiment 1-5

A uniaxially drawn film of polysulfone (hereinafter abbreviated to PSF)was used as the retardation film 2 in the configuration of FIGS. 1 and3A.

In this case, the ratio α of the optical anisotropy at a wavelength of450 nm with respect to the optical anisotropy at a wavelength of 590 nmwas 1.15.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 was set to 35° to 55°, theangle θ2 between the direction B1 of the slow axis of the retardationfilm 2 and the direction of rubbing C1 of the upper plane was set to 80°to 100°, the angle θ3 between the direction of rubbing C2 of the lowerplane and the direction A2 of the absorption axis (or polarization axis)of the lower polarizing plate 4 was set to 35° to 55°, combinations ofthe product Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10 and the retardation R of the retardation film2 were set up as shown in Table 5, and the change of color produced whena voltage was applied between the upper and lower electrodes 6 and 8 wasmeasured with a spectrophotometer.

                  TABLE 5                                                         ______________________________________                                        No.      Δn                                                                             d (μm)  Δn · d (μm)                                                         R (μm)                                  ______________________________________                                        1        0.13   7.0        0.91    0.7                                        2        0.18   7.0        1.26    1.2                                        3        0.20   7.0        1.4     1.2                                        4        0.20   7.0        1.4     1.4                                        5        0.20   7.0        1.4     1.6                                        6        0.23   7.0        1.61    1.2                                        7        0.23   7.0        1.61    1.4                                        8        0.23   7.0        1.61    1.6                                        9        0.24   8.0        1.92    1.2                                        10       0.24   8.0        1.92    1.4                                        11       0.24   8.0        1.92    1.6                                        ______________________________________                                    

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and at least two colors were displayed when avoltage was applied, provided that the retardation R of the retardationfilm 2 and the product Δn·d of the optical anisotropy Δn and thethickness d of the nematic liquid crystal 10 were in a predeterminedrelationship.

These results are shown in FIG. 10. In FIG. 10, a portion (a) is a rangewithin which the color tone at zero voltage is white or a non-colorclose thereto and at least two colors are displayed when a voltage isapplied, so that this is a range in which the previously described firstand second conditions are both satisfied.

Therefore, within the range (a) of FIG. 10, the color tone at zerovoltage was white or a non-color close thereto and at least two colorswere displayed when a voltage was applied. Conversely, outside the range(a) of FIG. 10, either the color tone at zero voltage was not white or anon-color close thereto, or display of at least two colors did not occurwhen a voltage was applied.

To demonstrate an example of conditions within the portion (a) of FIG.10, a liquid crystal cell 3 was used in which the optical anisotropy Δnof the nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm,in other words in which Δn·d was 1.61 μm, and the retardation R of theretardation film 2 was 1.4 μm. In this example, the color tone at zerovoltage was a bluish white, at an effective voltage of 2.22 V it wasblack, at 2.25 V it was blue, at 2.27 V it was a yellow-green, and at2.37 V it was pink. In other words, this is one set of conditions thatis most suitable for the liquid crystal device of this invention.

In addition, as an example of another set of conditions within theportion (a) of FIG. 10, a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.18 and thethickness d was 7 μm, in other words in which Δn·d was 1.26 μm, and theretardation R of the retardation film 2 was 1.2 μm. In this example, thecolor tone at zero voltage was a reddish white, at an effective voltageof 2.19 V it was orange, at 2.23 V it was blue, and at 2.26 V it wasgreen. In other words, this is one set of conditions that is mostsuitable for the liquid crystal device of this invention.

Conversely, to demonstrate conditions outside the range (a) of FIG. 10under which the color tone at zero voltage is not white or a non-colorclose thereto, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.2 and the thicknessd was 7 μm, in other words in which Δn·d was 1.4 μm, and the retardationR of the retardation film 2 was 1.6 μm, alternatively a liquid crystalcell 3 was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.24 and the thickness d was 8 μm, in other words inwhich Δn·d was 1.92 μm, and the retardation R of the retardation film 2was 1.4 μm; the color tone at zero voltage was black in the former caseand the color tone at zero voltage was yellow in the latter case. Inother words, these are conditions that are not suitable for the liquidcrystal device of this invention.

To further demonstrate conditions outside the range (a) of FIG. 10 underwhich display of at least two colors does not occur when a voltage isapplied although the color tone displayed at zero voltage is white or anon-color close thereto, a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.13 and thethickness d was 7 μm, in other words in which Δn·d was 0.91 μm, and theretardation R of the retardation film 2 was 0.7 μm; in this case, thecolor tone at zero voltage was a yellowish white, but the only changethat occurred when a voltage was applied was to orange. In other words,these are conditions that are not suitable for the liquid crystal deviceof this invention.

Embodiment 1-6

A uniaxially drawn film of PSF was used as the retardation film 2 in theconfiguration of FIGS. 1 and 3B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 was set to 35° to 55°, theangle θ2 between the direction B1 of the slow axis of the retardationfilm 2 and the direction of rubbing C1 of the upper plane was set to 80°to 100°, the angle θ3 between the direction of rubbing C2 of the lowerplane and the direction A2 of the absorption axis (or polarization axis)of the lower polarizing plate 4 was set to 35° to 55°, combinations ofthe product Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10 and the retardation R of the retardation film2 were set up as shown in Table 6, and the change of color produced whena voltage was applied between the upper and lower electrodes 6 and 8 wasmeasured with a spectrophotometer.

                  TABLE 6                                                         ______________________________________                                        No.      Δn                                                                             d (μm)  Δn · d (μm)                                                         R (μm)                                  ______________________________________                                        1        0.13   7.0        0.91    1.0                                        2        0.18   7.0        1.26    1.5                                        3        0.18   7.0        1.26    1.7                                        4        0.18   7.0        1.26    1.9                                        5        0.23   7.0        1.61    1.5                                        6        0.23   7.0        1.61    1.7                                        7        0.23   7.0        1.61    1.9                                        8        0.24   8.0        1.92    1.5                                        9        0.24   8.0        1.92    1.7                                        10       0.24   8.0        1.92    1.9                                        ______________________________________                                    

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and at least two colors were displayed when avoltage was applied, provided that the retardation R of the retardationfilm 2 and the product Δn·d of the optical anisotropy Δn and thethickness d of the nematic liquid crystal 10 were in a predeterminedrelationship.

These results are shown in FIG. 11. In FIG. 11, a portion (a) is a rangewithin which the color tone at zero voltage is white or a non-colorclose thereto and at least two colors are displayed when a voltage isapplied, so that this is a range in which the previously described firstand second conditions are both satisfied

Therefore, within the range (a) of FIG. 11, the color tone at zerovoltage was white or a non-color close thereto and at least two colorswere displayed when a voltage was applied. Conversely, outside the range(a) of FIG. 11, either the color tone at zero voltage was not white or anon-color close thereto, or color display of at least two colors did notoccur when a voltage was applied.

To demonstrate an example of the conditions within the range (a) of FIG.11, a liquid crystal cell 3 was used in which the optical anisotropy Δnof the nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm,in other words in which Δn·d was 1.61 μm, and the retardation R of theretardation film 2 was 1.7 μm. In this example, the color tone at zerovoltage was a yellowish white, at an effective voltage of 2.10 V it wasorange, at 2.15 V it was blue, and at 2.17 V it was green. In otherwords, this is one set of conditions that is most suitable for theliquid crystal device of this invention.

In addition, to demonstrate the boundary conditions at which it isassumed the color tone at zero voltage becomes white or a non-colorclose thereto within the portion (a) of FIG. 11, a liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the retardation film 2was 1.9 μm, alternatively a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.18 and thethickness d was 7 μm, in other words in which Δn·d was 1.26 μm, and theretardation R of the retardation film 2 was 1.5 μm; in these cases, thecolor tone at zero voltage became a reddish white. When a voltage wasapplied, color changes to orange, blue, and green occurred as thevoltage increased. In other words, these are boundary conditions for theliquid crystal device of this invention.

Conversely, to demonstrate conditions outside the range (a) of FIG. 11under which the color tone at zero voltage is not white or a non-colorclose thereto, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.18 and thethickness d was 7 μm, in other words in which Δn·d was 1.26 μm, and theretardation R of the retardation film 2 was 1.7 μm, alternatively aliquid crystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.24 and the thickness d was 8 μm, inother words in which Δn·d was 1.92 μm, and the retardation R of theretardation film 2 was 1.7 μm; and the color tone at zero voltage wasorange in the former case and the color tone at zero voltage was blue inthe latter case. In other words, these are conditions that are notsuitable for the liquid crystal device of this invention.

To further demonstrate conditions outside the range (a) of FIG. 11 underwhich display of at least two colors does not occur when a voltage isapplied although the color tone displayed at zero voltage is white or anon-color close thereto, a liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.13 and thethickness d was 7 μm, in other words in which Δn·d was 0.91 μm, and theretardation R of the retardation film 2 was 1 μm; in this case, thecolor tone at zero voltage was a bluish white, but the color changedonly to orange when a voltage was applied. In other words, these areconditions that are not suitable for the liquid crystal device of thisinvention.

EMBODIMENT 2

This embodiment gives examples of the use of two uniaxially drawnretardation films of PC as optically anisotropic substances.

A sectional view through a second reflective type of liquid crystaldevice to which this invention is applied is shown in FIG. 12.

In FIG. 12, reference number 1 denotes an upper polarizing plate,reference numbers 2a and 2b denote retardation films, reference number 3denotes a liquid crystal cell, reference number 4 denotes a lowerpolarizing plate, and reference number 5 denotes a reflective plate. Theconfiguration of the liquid crystal cell 3 is the same as that of FIG.1.

The relationships between the directions of the absorption axes (orpolarization axes) of the polarizing plates 1 and 4 of FIG. 12, thedirections of the slow axes of the retardation films 2a and 2b, and thedirections of rubbing of the upper and lower planes are shown in FIGS.13A and 13B.

FIGS. 13A and 13B are differentiated by the direction of the absorptionaxis (or polarization axis) of the upper polarizing plate 1. In thesefigures, A1 and A2 are the directions of the absorption axes (orpolarization axes) of the upper and lower polarizing plates 1 and 4, B1and B2 are the directions of the slow axes of the retardation films 2aand 2b, and C1 and C2 are the directions of rubbing of the upper andlower planes. In addition, T is the twist angle of the nematic liquidcrystal 10, θ1 is the angle between the direction A1 of the absorptionaxis (or polarization axis) of the upper polarizing plate 1 and thedirection B1 of the slow axis of the retardation film 2a, θ2 is theangle between the direction B2 of the slow axis of the retardation film2b and the direction of rubbing C1 of the upper plane, θ3 is the anglebetween the direction of rubbing C2 of the lower plane and the directionA2 of the absorption axis (or polarization axis) of the lower polarizingplate 4, and θ4 is the angle between the direction B1 of the slow axisof the retardation film 2a and the direction B2 of the slow axis of theretardation film 2b. θ1 is set to be more than 0° and less than 90°.

Embodiment 2-1

A uniaxially drawn film of PC was used as each of the retardation films2a and 2b in the configuration of FIGS. 12 and 13A.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2a and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, the angle θ2 between the direction B2 ofthe slow axis of the retardation film 2b and the direction of rubbing C1of the upper plane was set to 80° to 100°, and the angle θ4 between thedirection B1 of the slow axis of the retardation film 2a and thedirection B2 of the slow axis of the retardation film 2b was set to 0°to 20°. A liquid crystal cell 3 was used in which the optical anisotropyΔn of the nematic liquid crystal 10 was 0.23 and the thickness d was 7μm, in other words in which Δn·d was 1.61 μm, and the sum of the productΔn1·d1 of the optical anisotropy Δn1 and the thickness d1 of theretardation film 2a plus the product Δn2·d2 of the optical anisotropyΔn2 and the thickness d2 of the retardation film 2b (hereinafter calledthe retardation R for Embodiment 2) was set to 2 μm. As a result, thecolor tone at zero voltage was seen to be white or a non-color closethereto and color changes to orange, blue, and green occurred as thevoltage increased. The various colors could be perceived over a widerviewing angle than in the configuration of Embodiment 1-1 in which asingle uniaxially drawn film of PC was used.

Embodiment 2-2

A uniaxially drawn film of PC was used as each of the retardation films2a and 2b in the configuration of FIGS. 12 and 13B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2a and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, the angle θ2 between the direction B2 ofthe slow axis of the retardation film 2b and the direction of rubbing C1of the upper plane was set to 80° to 100°, and the angle θ4 between thedirection B1 of the slow axis of the retardation film 2a and thedirection B2 of the slow axis of the retardation film 2b was set to 0 to20°. A liquid crystal cell 3 was used in which the optical anisotropy Δnof the nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm,in other words in which Δn·d was 1.61 μm, and the retardation R of theretardation films 2a and 2b was 1.8 μm. As a result, the color tone atzero voltage was seen to be white or a non-color close thereto and colorchanges to black, blue, yellow-green, and pink occurred when a voltagewas applied. The various colors could be perceived over a wider viewingangle than in the configuration of Embodiment 1-2 in which a singleuniaxially drawn film of PC was used.

EMBODIMENT 3

This embodiment gives examples of the use of two uniaxially drawnretardation films of PC as optically anisotropic substances.

A sectional view through a third reflective type of liquid crystaldevice to which this invention is applied is shown in FIG. 14. In FIG.14, reference number 1 denotes an upper polarizing plate, referencenumbers 2a and 2b denote retardation films, reference number 3 denotes aliquid crystal cell, reference number 4 denotes a lower polarizingplate, and reference number 5 denotes a reflective plate. Theconfiguration of the liquid crystal cell 3 is the same as that of FIG.1.

The retardation films 2a and 2b were disposed between the upperpolarizing plate 1 and the liquid crystal cell 3 in the above describedEmbodiment 2, but in Embodiment 3, the retardation film 2a is disposedbetween the upper polarizing plate 1 and the liquid crystal cell 3, andthe retardation film 2b is disposed between the liquid crystal cell 3and the lower polarizing plate.

The mutual relationships between the directions of the absorption axes(or polarization axes) of the polarizing plates 1 and 4 of FIG. 14, thedirections of the slow axes of the retardation films 2a and 2b, and thedirections of rubbing of the upper and lower planes are shown in FIGS.15A and 15B. FIGS. 15A and 15B are differentiated by the direction ofthe absorption axis (or polarization axis) of the upper polarizing plate1.

In FIGS. 15A and 15B, A1 and A2 are the directions of the absorptionaxes (or polarization axes) of the upper and lower polarizing plates 1and 4, B1 and B2 are the directions of the slow axes of the retardationfilms 2a and 2b, and C1 and C2 are the directions of rubbing of theupper and lower planes. In addition, T is the twist angle of the nematicliquid crystal 10, θ1 is the angle between the direction A1 of theabsorption axis (or polarization axis) of the upper polarizing plate 1and the direction B1 of the slow axis of the retardation film 2a, 62 isthe angle between the direction B1 of the slow axis of the retardationfilm 2a and the direction of rubbing C1 of the upper plane, θ5 is theangle between the direction of rubbing C2 of the lower plane and thedirection B2 of the slow axis of the retardation film 2b, and 66 is theangle between the direction B2 of the slow axis of the retardation film2b and the direction A2 of the absorption axis (or polarization axis) ofthe lower polarizing plate 4. θ1 is set to be more than 0° and less than90°.

Embodiment 3-1

A uniaxially drawn film of PC was used as each of the retardation films2a and 2b in the configuration of FIGS. 14 and 15A.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2a and the angle θ6 between thedirection A2 of the absorption axis (or polarization axis) of the lowerpolarizing plate 4 of the retardation film 2b were both set to 35° to55°, and the angle θ2 between the direction B1 of the slow axis of theretardation film 2a and the direction of rubbing C1 of the upper planeand the angle θ5 between the direction of rubbing C2 of the lower planeand the direction B2 of the slow axis of the retardation film 2b wereboth set to 80° to 100°.

A liquid crystal cell 3 was used in which the optical anisotropy Δn ofthe nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the sum of the product Δn1·d1of the optical anisotropy Δn1 and the thickness d1 of the retardationfilm 2a plus the product Δn2·d2 of the optical anisotropy Δn2 and thethickness d2 of the retardation film 2b (hereinafter called theretardation R for Embodiment 3) was set to 2 μm. As a result, the colortone at zero voltage was seen to be white or a non-color close theretoand color changes to orange, blue, and green occurred as the voltageincreased. In a similar manner to that of Embodiment 2-1, the variouscolors could be perceived over a wider viewing angle than in theconfiguration of Embodiment 1-1 in which a single uniaxially drawn filmof PC was used.

Embodiment 3-2

A uniaxially drawn film of PC was used as each of the retardation films2a and 2b in the configuration of FIGS. 14 and 15B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2a and the angle θ6 between thedirection A2 of the absorption axis (or polarization axis) of the lowerpolarizing plate 4 of the retardation film 2b were both set to 350° to55°, and the angle θ2 between the direction B1 of the slow axis of theretardation film 2a and the direction of rubbing C1 of the upper planeand the angle θ5 between the direction of rubbing C2 of the lower planeand the direction B2 of the slow axis of the retardation film 2b wereboth set to 80° to 100°. A liquid crystal cell 3 was used in which theoptical anisotropy Δn of the nematic liquid crystal 10 was 0.23 and thethickness d was 7 μm, in other words in which Δn·d was 1.61 μm, and theretardation R of the retardation film 2a was 1.8 μm. As a result, thecolor tone at zero voltage was seen to be white or a non-color closethereto and color changes to black, blue, yellow-green, and pinkoccurred when a voltage was applied.

In a similar manner to that of the above Embodiment 2-2, the variouscolors could be perceived over a wider viewing angle than in theconfiguration of Embodiment 1-2 in which a single uniaxially drawn filmof PC was used.

EMBODIMENT 4

This embodiment gives examples of the use of six uniaxially drawnretardation films of PC as optically anisotropic substances.

A sectional view through a fourth reflective type of liquid crystaldevice to which this invention is applied is shown in FIG. 16. In FIG.16, reference number 1 denotes an upper polarizing plate, referencenumbers 2a to 2f denote retardation films, reference number 3 denotes aliquid crystal cell, reference number 4 denotes a lower polarizingplate, and reference number 5 denotes a reflective plate. Theconfiguration of the liquid crystal cell 3 is the same as that of FIG.1.

The mutual relationships between the directions of the absorption axes(or polarization axes) of the polarizing plates 1 and 4 of FIG. 16, thedirections of the slow axes of the retardation films 2a to 2f, and thedirections of rubbing of the upper and lower planes are shown in FIGS.17A and 17B. FIGS. 17A and 17B are differentiated by the direction ofthe absorption axis (or polarization axis) of the upper polarizing plate1.

In FIGS. 17A and 17B, A1 and A2 are the directions of the absorptionaxes (or polarization axes) of the upper and lower polarizing plates 1and 4, B1 to B6 are the directions of the slow axes of the retardationfilms 2a to 2f, and C1 and C2 are the directions of rubbing of the upperand lower planes. In addition, T is the twist angle of the nematicliquid crystal 10, θ1 is the angle between the direction A1 of theabsorption axis (or polarization axis) of the upper polarizing plate 1and the direction B6 of the slow axis of the retardation film 2f, θ2 isthe angle between the direction B1 of the slow axis of the retardationfilm 2a and the direction of rubbing C1 of the upper plane, θ3 is theangle between the direction of rubbing C2 of the lower plane and thedirection A2 of the absorption axis (or polarization axis) of the lowerpolarizing plate 4, θ41 is the angle between the direction B1 of theslow axis of the retardation film 2a and the direction B2 of the slowaxis of the retardation film 2b, and θ42 to θ45 are similarly the anglesbetween the directions of the slow axes of each pair of retardationfilms 2b and 2c, 2c and 2d, 2d and 2e, and 2e and 2f. θ1 is set to bemore than 0° and less than 90°.

Embodiment 4-1

A uniaxially drawn film of PC was used as each of the retardation films2a to 2f in the configuration of FIGS. 16 and 17A.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B6of the slow axis of the retardation film 2f and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, the angle θ2 between the direction B1 ofthe slow axis of the retardation film 2a and the direction of rubbing C1of the upper plane was set to 80° to 100°, and the angles θ41 to θ45between the directions of the slow axes of the retardation films 2a and2b, 2b and 2c, 2c and 2d, 2d and 2e, and 2e and 2f were all set to 40°.A liquid crystal cell 3 was used in which the optical anisotropy Δn ofthe nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the total sum of the productΔn1·d1 of the optical anisotropy Δn1 and the thickness d1 of theretardation film 2a plus the product Δn2·d2 of the optical anisotropyΔn2 and the thickness d2 of the retardation film 2b plus, in a similarmanner, the product Δnj·dj (where j is an integer of 6 or less) of theoptical anisotropy Δnj and the thickness dj of each of the retardationfilms 2c to 2f (hereinafter called the retardation R for Embodiment 4)was 2 μm.

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and color changes to orange, blue, and greenoccurred as the voltage increased. The various colors could be perceivedover a wider viewing angle than in the configurations of Embodiments 2-1and 3-1 in which two uniaxially drawn films of PC were used.

Embodiment 4-2

A uniaxially drawn film of PC was used as each of the retardation films2a to 2f in the configuration of FIGS. 16 and 17B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B6of the slow axis of the retardation film 2f and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, the angle θ2 between the direction B1 ofthe slow axis of the retardation film 2a and the direction of rubbing C1of the upper plane was set to 80° to 100°, and the angles θ41 to θ45between the directions of the slow axes of the retardation films 2a and2b, 2b and 2c, 2c and 2d, 2d and 2e, and 2e and 2f were all set to 40°.A liquid crystal cell 3 was used in which the optical anisotropy Δn ofthe nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the retardation R of theretardation films 2a to 2f was 1.8 μm. As a result, the color tone atzero voltage was seen to be white or a non-color close thereto and colorchanges to black, blue, yellow-green, and pink occurred when a voltagewas applied. The various colors could be perceived over a wider viewingangle than in the configurations of Embodiments 2-2 and 3-2 in which twouniaxially drawn films of PC were used.

EMBODIMENT 5

This embodiment gives examples of the use of an NZ retardation film ofPC as the optically anisotropic substance.

A sectional view through a fifth reflective type of liquid crystaldevice to which this invention is applied is shown in FIG. 18. In FIG.18, reference number 1 denotes an upper polarizing plate, referencenumber 20 denotes an NZ retardation film, reference number 3 denotes aliquid crystal cell, reference number 4 denotes a lower polarizingplate, and reference number 5 denotes a reflective plate. Theconfiguration of the liquid crystal cell 3 is the same as that of FIG.1.

An NZ retardation film is a retardation film having different values ofny and nz, where the refractive index thereof in the direction of themaximum refractive index parallel to the film surface is nx, therefractive index thereof in a direction perpendicular to nx and parallelto the film surface is ny, and the refractive index thereof in the filmthickness direction is nz. In this case, the value of (nx-nz)/(nx-ny) isdefined as the NZ factor.

The mutual relationships between the directions of the absorption axes(or polarization axes) of the polarizing plates 1 and 4 of FIG. 18, thedirection of the slow axis of the NZ retardation film 20, and thedirections of rubbing of the upper and lower planes are shown in FIGS.19A and 19B. FIGS. 19A and 19B are differentiated by the direction ofthe absorption axis (or polarization axis) of the upper polarizing plate1.

In FIGS. 19A and 19B, A1 and A2 are the directions of the absorptionaxes (or polarization axes) of the upper and lower polarizing plates 1and 4, B1 is the direction of the slow axis of the NZ retardation film20, and C1 and C2 are the directions of rubbing of the upper and lowerplanes.

In addition, T is the twist angle of the nematic liquid crystal 10, θ1is the angle between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the NZ retardation film 20, θ2 is the angle betweenthe direction B1 of the slow axis of the NZ retardation film 20 and thedirection of rubbing C1 of the upper plane, and θ3 is the angle betweenthe direction of rubbing C2 of the lower plane and the direction A2 ofthe absorption axis (or polarization axis) of the lower polarizing plate4. θ1 is set to be more than 0° and less than 90.degree.

Embodiment 5-1

NZ retardation films of PC having NZ factors of 0 to 1 were used as theNZ retardation film 20 in the configuration of FIGS. 18 and 19A.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the NZ retardation film 20 and the angle θ3 betweenthe direction of rubbing C2 of the lower plane and the direction A2 ofthe absorption axis (or polarization axis) of the lower polarizing plate4 were both set to 35° to 55°, and the angle θ2 between the direction B1of the slow axis of the NZ retardation film 20 and the direction ofrubbing C1 of the upper plane was set to 80° to 100°. A liquid crystalcell 3 was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, the product Δn1·d1 of the optical anisotropy Δn1and the thickness d1 of the NZ retardation film 20 (hereinafter calledthe retardation R for Embodiment 5) was 2 μm. As a result, the colortone of the display viewed from the front irrespective of the value ofthe NZ factor was such that the color tone at zero voltage was seen tobe white or a non-color close thereto, and color changes that wereexactly the same as those to orange, blue, and green shown in the colorchart of FIG. 4 occurred when a voltage was applied.

Evaluations were made of the visibility of color tone on a scale of oneto ten when NZ retardation films with NZ factors of 0 to 1 were used andthe angle of view was shifted through 30° in the forward, rearward, andlateral directions with respect to the front, with the results being asshown in FIG. 20. The various colors could be seen over a wide viewingangle range in the forward and lateral directions when the NZ factor was0.7 or less, and the various colors could be seen over a wide viewingangle in the rearward direction when the NZ factor was 0.6 or less. Inother words, the various colors could be seen over a wide viewing anglewhen the NZ factor was 0.7 or less, and over an even wider viewing anglewhen the NZ factor was between 0.1 and 0.6.

Embodiment 5-2

NZ retardation films of PC having NZ factors of 0 to 1 were used as theNZ retardation film 20 in the configuration of FIGS. 18 and 19B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the NZ retardation film 20 and the angle θ3 betweenthe direction of rubbing C2 of the lower plane and the direction A2 ofthe absorption axis (or polarization axis) of the lower polarizing plate4 were both set to 35° to 55°, the angle θ2 between the direction B1 ofthe slow axis of the NZ retardation film 20 and the direction of rubbingC1 of the upper plane was set to 80° to 100°. A liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the NZ retardation film20 was 1.8 μm. As a result, the color tone of the display viewed fromthe front irrespective of the value of the NZ factor was such that thecolor tone at zero voltage was seen to be white or a non-color closethereto, and color changes that were exactly the same as those to black,blue, yellow-green, and pink shown in the color chart of the curve (b)of FIG. 6 occurred when a voltage was applied.

When the angle of view was shifted through 30° in the upward, downward,and lateral directions with respect to the front, in a similar manner tothat shown in FIG. 20, the various colors could be seen over a wideviewing angle range in the downward and lateral directions when the NZfactor was 0.7 or less, and the various colors could be seen over a wideviewing angle range in the upward direction when the NZ factor was 0.6or less. In other words, the various colors could be seen over a wideviewing angle range when the NZ factor was 0.7 or less, and over an evenwider viewing angle when the NZ factor was between 0.1 and 0.6.

In Embodiment 5, NZ retardation films of PC were used as the NZretardation film 20 but the invention is not limited thereto; similarresults could be obtained by superimposing two or more types ofretardation film, such as a uniaxially drawn film of polystyrene with anNZ factor of 0 and a uniaxially drawn film of PC with an NZ factor of 1,to give an average value of NZ factor that lies within the above range.

EMBODIMENT 6

This embodiment gives examples of the use of a twisted retardation filmas the optically anisotropic substance.

A sectional view through a sixth reflective type of liquid crystaldevice to which this invention is applied is shown in FIG. 21. In FIG.21, reference number 1 denotes an upper polarizing plate, referencenumber 22 denotes a twisted retardation film, reference number 3 denotesa liquid crystal cell, reference number 4 denotes a lower polarizingplate, and reference number 5 denotes a reflective plate. Theconfiguration of the liquid crystal cell 3 is the same as that of FIG.1.

A twisted retardation film is a retardation film that is characterizedin that the direction of the slow axis thereof is parallel to the filmsurface and also the twist thereof varies continuously with respect tothe film thickness direction.

The mutual relationships between the directions of the absorption axes(or polarization axes) of the polarizing plates 1 and 4 of FIG. 21, thedirection of the slow axis of the twisted retardation film 22, and thedirections of rubbing of the upper and lower planes are shown in FIGS.22A and 22B.

FIGS. 22A and 22B are differentiated by the direction of the absorptionaxis (or polarization axis) of the upper polarizing plate 1. In FIGS.22A and 22B, A1 and A2 are the directions of the absorption axes (orpolarization axes) of the upper and lower polarizing plates 1 and 4, B1is the direction of the slow axis at the surface of the twistedretardation film 22 in contact with the upper polarizing plate 1, B2 isthe direction of the slow axis at the surface of the twisted retardationfilm 22 in contact with the liquid crystal cell 3, and C1 and C2 are thedirections of rubbing of the upper and lower planes.

In addition, T1 is the twist angle of the nematic liquid crystal 10, T2is the twist angle of the slow axis of the twisted retardation film 22,θ1 is the angle between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B2of the slow axis of the twisted retardation film 22, θ2 is the anglebetween the direction B2 of the slow axis of the twisted retardationfilm 22 and the direction of rubbing C1 of the upper plane, and θ3 isthe angle between the direction of rubbing C2 of the lower plane and thedirection A2 of the absorption axis (or polarization axis) of the lowerpolarizing plate 4. θ1 is set to be more than 0° and less than 90°.

Embodiment 6-1

A twisted retardation film in which the ratio α of the opticalanisotropy at a wavelength of 450 nm with respect to the opticalanisotropy at a wavelength of 590 nm was 1.09 was used as the twistedretardation film 22 in the configuration of FIGS. 21 and 22A.

The twist angle T1 of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the twisted retardation film 22 and the angle θ3between the direction of rubbing C2 of the lower plane and the directionA2 of the absorption axis (or polarization axis) of the lower polarizingplate 4 were both set to 35° to 55°, and the angle θ2 between thedirection B2 of the slow axis of the twisted retardation film 22 and thedirection of rubbing C1 of the upper plane was set to 80° to 100°. Aliquid crystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the product Δn1·d1 of theoptical anisotropy Δn1 and the thickness d1 of the twisted retardationfilm 22 (hereinafter called the retardation R for Embodiment 6) was setto 2 μm. Four values were used for the twist angle T2 of the slow axisof the twisted retardation film 22:120°, 160°, 200°, and 240°. As aresult, the color tone at zero voltage in every example was seen to bewhite or a non-color close thereto and color changes to orange, blue,and green occurred as the voltage increased. A particularly vivid colortone was produced when the twist angle T2 of the slow axis of thetwisted retardation film 22 was 240°.

Embodiment 6-2

A twisted retardation film in which the ratio α of the opticalanisotropy at a wavelength of 450 nm with respect to the opticalanisotropy at a wavelength of 590 nm was 1.17 was used as the twistedretardation film 22 in the configuration of FIGS. 21 and 22A.

The twist angle T1 of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the twisted retardation film 22 and the angle θ3between the direction of rubbing C2 of the lower plane and the directionA2 of the absorption axis (or polarization axis) of the lower polarizingplate 4 were both set to 35° to 55°, and the angle θ2 between thedirection B2 of the slow axis of the twisted retardation film 22 and thedirection of rubbing C1 of the upper plane was set to 80° to 100°. Aliquid crystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the retardation R of thetwisted retardation film 22 was 1.8 μm.

Four values were used for the twist angle T2 of the slow axis of thetwisted retardation film 22:120°, 160°, 200°, and 240°. As a result, thecolor tone at zero voltage in every example was seen to be white or anon-color close thereto and color changes to orange, blue, and greenoccurred as the voltage increased. A particularly vivid color tone wasproduced when the twist angle T2 of the slow axis of the twistedretardation film 22 was 240°.

Embodiment 6-3

A twisted retardation film in which the ratio α of the opticalanisotropy at a wavelength of 450 nm with respect to the opticalanisotropy at a wavelength of 590 nm was 1.09 was used as the twistedretardation film 22 in the configuration of the configuration of FIGS.21 and 22B. In addition, the twist angle T1 of the nematic liquidcrystal 10 was set to 240°, the angle θ1 between the direction A1 of theabsorption axis (or polarization axis) of the upper polarizing plate 1and the direction B1 of the slow axis of the twisted retardation film 22and the angle θ3 between the direction of rubbing C2 of the lower planeand the direction A2 of the absorption axis (or polarization axis) ofthe lower polarizing plate 4 were both set to 35° to 55°, the angle θ2between the direction B2 of the slow axis of the twisted retardationfilm 22 and the direction of rubbing C1 of the upper plane was set to80° to 100°. A liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.23 and thethickness d was 7 μm, in other words in which Δn·d was 1.61 μm, and theretardation R of the twisted retardation film 22 was 1.8 μm. Four valueswere used for the twist angle T2 of the slow axis of the twistedretardation film 22:120°, 160°, 200°, and 240°. As a result, the colortone at zero voltage in every example was seen to be white or anon-color close thereto and color changes to black, blue, yellow-green,and pink occurred when a voltage was applied. A particularly vivid colortone was produced when the twist angle T2 of the slow axis of thetwisted retardation film 22 was 240°.

Embodiment 6-4

A twisted retardation film in which the ratio α of the opticalanisotropy at a wavelength of 450 nm with respect to the opticalanisotropy at a wavelength of 590 nm was 1.17 was used in place of theretardation film 2 in the configuration of FIGS. 1 and 19B.

The twist angle T1 of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the twisted retardation film and the angle θ3between the direction of rubbing C2 of the lower plane and the directionA2 of the absorption axis (or polarization axis) of the lower polarizingplate 4 were both set to 35° to 55°, the angle θ2 between the directionB1 of the slow axis of the twisted retardation film and the direction ofrubbing C1 of the upper plane was set to 80° to 100°. A liquid crystalcell 3 was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the twisted retardationfilm was 1.6 μm. Four values were used for the twist angle T2 of theslow axis of the twisted retardation film:120°, 160°, 200°, and 240°. Asa result, the color tone at zero voltage in every example was seen to bewhite or a non-color close thereto and color changes to black, blue,yellow-green, and pink occurred when a voltage was applied. Aparticularly vivid color tone was produced when the twist angle T2 ofthe slow axis of the twisted retardation film was 240°.

The nematic liquid crystal 10 used in Embodiment 6 had an opticalanisotropy Δn of 0.23 and the ratio α of its optical anisotropy at awavelength of 450 nm with respect to its optical anisotropy at awavelength of 590 nm was 1.17.

Embodiment 6-4 was a specific example in which the ratio α of theoptical anisotropy of the nematic liquid crystal 10 at a wavelength of450 nm with respect to the optical anisotropy thereof at a wavelength of590 nm was substantially the same as the ratio α of the opticalanisotropy of the twisted retardation film at a wavelength of 450 nmwith respect to the optical anisotropy thereof at a wavelength of 590nm; in that case, when the twist angle T1 of the nematic liquid crystal10 and the twist angle T2 of the twisted retardation film hadsubstantially the same degrees but were twisted inversely and theproduct Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10 and the retardation R of the twistedretardation film were substantially the same, the color tone at zerovoltage was seen to be white or a non-color close thereto and colorchanges to black, blue, yellow-green, and pink occurred when a voltagewas applied.

In addition, although only a twisted retardation film was disposedbetween the upper polarizing plate 1 and the liquid crystal cell 3 inEmbodiment 6, this invention is not limited to this configuration andthus a combination of a twisted retardation film and a uniaxially drawnretardation film could be disposed therebetween instead.

EMBODIMENT 7

This embodiment gives examples of the use of a second liquid crystalcell as the optically anisotropic substance.

A sectional view through a seventh reflective type of liquid crystaldevice to which this invention is applied is shown in FIG. 23. In FIG.23, reference number 1 denotes an upper polarizing plate, referencenumber 26 denotes a second liquid crystal cell, reference number 3denotes a liquid crystal cell, reference number 4 denotes a lowerpolarizing plate, and reference number 5 denotes a reflective plate. Theconfiguration of each of the liquid crystal cell 3 and the second liquidcrystal cell 26 is the same as that of the liquid crystal cell 3 ofFIG. 1. Note, however, that there the second liquid crystal cell 26 doesnot have the upper and lower electrodes 6 and 8.

The mutual relationships between the directions of the absorption axes(or polarization axes) of the polarizing plates 1 and 4 of FIG. 23, thedirections of rubbing of the upper and lower planes of the second liquidcrystal cell 26, and the directions of rubbing of the upper and lowerplanes of the liquid crystal cell 3 are shown in FIGS. 24A and 24B.

In FIGS. 24A and 24B, A1 and A2 are the directions of the absorptionaxes (or polarization axes) of the upper and lower polarizing plates 1and 4 of FIG. 23, B1 and B2 are the directions of rubbing of the upperand lower planes of the second liquid crystal cell 26, and C1 and C2 arethe directions of rubbing of the upper and lower planes of the liquidcrystal cell 3. In addition, T1 is the twist angle of the nematic liquidcrystal 10 filling the liquid crystal cell 3, T2 is the twist angle ofthe nematic liquid crystal 10 filling the second liquid crystal cell 26,θ1 is the angle between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction ofrubbing B1 of the upper plane of the second liquid crystal cell 26, θ2is the angle between the direction of rubbing B2 of the lower plane ofthe second liquid crystal cell 26 and the direction of rubbing C1 of theupper plane of the liquid crystal cell 3, and θ3 is the angle betweenthe direction of rubbing C2 of the lower plane of the liquid crystalcell 3 and the direction A2 of the absorption axis (or polarizationaxis) of the lower polarizing plate 4. θ1 is set to be more than 0° andless than 90°.

Embodiment 7-1

With the configuration of FIGS. 23 and 24 A, the twist angle T1 of thenematic liquid crystal 10 filling the liquid crystal cell 3 was set to240° and the twist angle T2 of the nematic liquid crystal 10 filling thesecond liquid crystal cell 26 was set to 0°.

In other words, this was a homogeneous alignment. The angle θ1 betweenthe direction A1 of the absorption axis (or polarization axis) of theupper polarizing plate 1 and the direction of rubbing B1 of the upperplane of the second liquid crystal cell 26 and the angle θ3 between thedirection of rubbing C2 of the lower plane of the liquid crystal cell 3and the direction A2 of the absorption axis (or polarization axis) ofthe lower polarizing plate 4 were both set to 35° to 55°, and the angleθ2 between the direction of rubbing B2 of the lower plane of the secondliquid crystal cell 26 and the direction of rubbing C1 of the upperplane of the liquid crystal cell 3 was set to 80° to 100°. The opticalanisotropy Δn of the nematic liquid crystal 10 filling the liquidcrystal cell 3 was 0.23 and the thickness d thereof was 7 μm, in otherwords Δn·d was 1.61 μm, and the optical anisotropy Δn of the nematicliquid crystal 10 filling the liquid crystal cell 26 was 0.13 and thethickness d thereof was 15 μm, in other words Δn·d was 1.95 μm. As aresult, the color tone at zero voltage was seen to be white or anon-color close thereto and color changes to orange, blue, and greenoccurred when a voltage was applied.

Embodiment 7-2

With the configuration of FIGS. 23 and 24B, the twist angle T1 of thenematic liquid crystal 10 filling the liquid crystal cell 3 was set to240° and the twist angle T2 of the nematic liquid crystal 10 filling thesecond liquid crystal cell 26 was also set to 240°. The angle θ1 betweenthe direction A1 of the absorption axis (or polarization axis) of theupper polarizing plate 1 and the direction of rubbing B1 of the upperplane of the second liquid crystal cell 26 and the angle θ3 between thedirection of rubbing C2 of the lower plane of the liquid crystal cell 3and the direction A2 of the absorption axis (or polarization axis) ofthe lower polarizing plate 4 were both set to 35° to 55°, and the angleθ2 between the direction of rubbing B2 of the lower plane of the secondliquid crystal cell 26 and the direction of rubbing C1 of the upperplane of the liquid crystal cell 3 was set to 80° to 100°. The opticalanisotropy Δn of the nematic liquid crystal 10 filling the liquidcrystal cell 3 was 0.23 and the thickness d thereof was 7 μm, in otherwords Δn·d was 1.61 μm, and the optical anisotropy Δn of the nematicliquid crystal 10 filling the liquid crystal cell 26 was 0.23 and thethickness d thereof was 7 μm, in other words Δn·d was 1.61 μm.

As a result, the color tone at zero voltage was seen to be white or anon-color close thereto and color changes to black, blue, yellow-green,and pink occurred when a voltage was applied.

In Embodiment 7, the ratio of the nematic-isotropic phase transitiontemperature of the nematic liquid crystal 10 filling the second liquidcrystal cell 26 with respect to the nematic-isotropic phase transitiontemperature of the nematic liquid crystal 10 filling the first liquidcrystal cell 3 is within the range of 0.8 to 1.2. In addition, thesenematic-isotropic phase transition temperature were both at least 80° C.In these examples, a liquid crystal device was obtained in which thecolor tone at zero voltage was seen to be white or a non-color closethereto within at least the range of -20° to 70°, and there was hardlyany change in external color with changes in temperature. Instead ofusing a second liquid crystal cell, it is clear that similar resultscould be obtained by using a retardation film with a retardation thathas substantially the same temperature dependency of the retardation Ras that of a liquid crystal cell, such as a retardation film in whichliquid crystal polymers are aligned horizontally or twisted.

With this invention, when the means capable of selecting at least threevalues of voltage to be applied between the pair of electrode substratesis further defined as a time division drive circuit that is capable ofapplying at least one other voltage between a selected voltage and anon-selected voltage, in addition to the selected voltage and thenon-selected voltage, it has been shown that the color tone at zerovoltage is white or a non-color close thereto and at least two colorsare displayed when a voltage is applied, provided that the liquidcrystal cell satisfies the following relationship: ##EQU4##

This is proved below with the aid of embodiments.

EMBODIMENT 8

This embodiment gives examples of the use of a time division drivecircuit as the drive circuit.

Embodiment 8-1

A time division drive circuit was used as the drive circuit 15 in theconfiguration of FIGS. 1 and 3A, and the relationships between theproduct Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10, the ratio P of the off-voltage to theon-voltage, and the steepness ratio β of the liquid crystal cell 3 wereinvestigated.

The steepness ratio β of the liquid crystal cell 3 is the ratio of thevoltage at which the capacitance of the liquid crystal cell 3 is 0.3 tothat voltage at which it is 0.1, when the capacitance of the liquidcrystal cell 3 is 0 for a voltage of 0.5 V applied between the upper andlower electrodes 6 and 8 and that capacitance is 1 for a voltage of 25V.

In addition, the ratio P of the off-voltage to the on-voltage isexpressed as follows, when the duty ratio is 1/N and the bias ratio is1/B: ##EQU5##

Therefore, if the drive is at the optimal bias at duty ratios of 1/64,1/120, 1/240, 1/480, the corresponding values of the ratio P of theoff-voltage to the on-voltage are 1.13, 1.1, 1.07 , 1.05.

A uniaxially drawn film of PC was used as the retardation film 2 in theabove described configuration. The twist angle T of the nematic liquidcrystal 10 was set to 240°, both the angle θ1 between the direction A1of the absorption axis (or polarization axis) of the upper polarizingplate 1 and the direction B1 of the slow axis of the retardation film 2and the angle θ3 between the direction of rubbing C2 of the lower planeand the direction A2 of the absorption axis (or polarization axis) ofthe lower polarizing plate 4 were set to 35° to 55°, and the angle θ2between the direction B1 of the slow axis of the retardation film 2 andthe direction of rubbing C1 of the upper plane was set to 80° to 100°.In addition, combinations of the product Δn·d of the optical anisotropyΔn and the thickness d of the nematic liquid crystal 10, the retardationR of the retardation film 2, the steepness ratio β of the liquid crystalcell 3 were used as shown in Table 7, and the change of color producedwhen a voltage was applied was measured with a spectrophotometer. Theresults are shown in FIG. 26.

                  TABLE 7                                                         ______________________________________                                        No.    Δn d (μm)                                                                             Δn · d (μm)                                                           R (μm)                                                                           β                                ______________________________________                                        1      0.20     6.0     1.20      1.55  1.06                                  2      0.20     6.0     1.20      1.55  1.08                                  3      0.20     6.0     1.20      1.55  1.10                                  4      0.20     6.0     1.20      1.55  1.12                                  5      0.23     6.0     1.38      1.75  1.06                                  6      0.23     6.0     1.38      1.75  1.08                                  7      0.23     6.0     1.38      1.75  1.10                                  8      0.23     6.0     1.38      1.75  1.12                                  9      0.23     7.0     1.61      2.00  1.06                                  10     0.23     7.0     1.61      2.00  1.08                                  11     0.23     7.0     1.61      2.00  1.10                                  12     0.23     7.0     1.61      2.00  1.12                                  13     0.26     7.0     1.82      2.15  1.06                                  14     0.26     7.0     1.82      2.15  1.08                                  15     0.26     7.0     1.82      2.15  1.10                                  16     0.26     7.0     1.82      2.15  1.12                                  ______________________________________                                    

In FIG. 26, triangles represent samples that exhibited color changesfrom white or a non-color close thereto, to orange, blue, and greenwhile the voltage varied from the off-voltage to the on-voltage when theratio P of the off-voltage to the on-voltage was 1.13 (when the dutyratio was set to 1/64 and the bias ratio to 1/9), and crosses representsamples that changed color imperfectly.

In addition, hollow circles represent samples that exhibited colorchanges from white or a non-color close thereto, to orange, blue, andgreen while the voltage varied from the off-voltage to the on-voltagewhen the ratio P of the off-voltage to the on-voltage was 1.1 (when theduty ratio was set to 1/120 and the bias ratio to 1/12), and squaresrepresent samples that exhibited color changes from white or a non-colorclose thereto, to orange, blue, and green while the voltage varied fromthe off-voltage to the on-voltage even though the ratio P of theoff-voltage to the on-voltage was 1.07 (when the duty ratio was set to1/240 and the bias ratio to 1/17). Furthermore, solid circles representsamples that exhibited color changes from white or a non-color closethereto, to orange, blue, and green while the voltage varied from theoff-voltage to the on-voltage even though the ratio P of the off-voltageto the on-voltage was 1.05 (when the duty ratio was set to 1/480 and thebias ratio to 1/23).

The above results show that the color tone at zero voltage is white or anon-color close thereto and color changes to the three colors of orange,blue, and green occur when a voltage is applied, provided that therelationships between the product Δn·d of the optical anisotropy Δn andthe thickness d of the nematic liquid crystal 10, the ratio P of theoff-voltage to the on-voltage, and the steepness ratio β of the liquidcrystal cell 3 satisfy the following relationship: ##EQU6## It isnecessary to satisfy the relationship above in order to implement thecolor changes from white through to green.

A time division drive circuit was used to provide a pulse widthmodulation drive in eight steps with the duty ratio set to 1/240 and thebias ratio set to 1/1.7 for a liquid crystal cell 3 in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.23 and thethickness d was 7 μm, in other words in which Δn·d was 1.61 μm, theretardation R of the retardation film 2 was 2 μm, and the steepnessratio β of the liquid crystal cell 3 was 1.08, and the colors obtainedat each of these steps were as shown in FIG. 27. The colors white, paleorange, dark orange, red-purple, blue-purple, blue, blue-green, andgreen were displayed at each of these steps.

It should be noted, however, that the effective voltage at each of thesteps when this stepped pulse drive was performed is given by: ##EQU7##In this case, V_(L/F) is the effective voltage in an F-step drive (whereF is a positive integer) at an Lth level (where L is an integer from 0to F-1), V_(O/F) is the off-voltage, and V.sub.(F-1)/F is theon-voltage. In addition, VOP is the drive voltage when the duty ratio is1/N and the bias ratio is 1/B. The effective voltage at each step of aframe rate control drive is expressed by the same equation and similarresults can be obtained thereby. Similar results can equally well beobtained by the use of a combination of a pulse width modulation driveand a frame rate control drive.

Embodiment 8-2

A time division drive circuit was used as the drive circuit 15 in theconfiguration of FIGS. 1 and 3B, and the relationships between theproduct Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10, the ratio P of the off-voltage to theon-voltage, and the steepness ratio β of the liquid crystal cell 3 wereinvestigated.

A uniaxially drawn film of PC was used as the retardation film 2 in theabove described configuration. The twist angle T of the nematic liquidcrystal 10 was set to 240°, the angle θ1 between the direction A1 of theabsorption axis (or polarization axis) of the upper polarizing plate 1and the direction B1 of the slow axis of the retardation film 2 and theangle θ3 between the direction of rubbing C2 of the lower plane and thedirection A2 of the absorption axis (or polarization axis) of the lowerpolarizing plate 4 were both set to 35° to 55°, and the angle θ2 betweenthe direction B1 of the slow axis of the retardation film 2 and thedirection of rubbing C1 of the upper plane was set to 80° to 100°. Inaddition, combinations of the product Δn·d of the optical anisotropy Δnand the thickness d of the nematic liquid crystal 10, the retardation Rof the retardation film 2, the steepness ratio β of the liquid crystalcell 3 were used as shown in Table 8, and the change of color producedwhen a voltage was applied was measured with a spectrophotometer. Theresults are shown in FIG. 28.

                  TABLE 8                                                         ______________________________________                                        No.    Δn d (μm)                                                                             Δn · d (μm)                                                           R (μm)                                                                           β                                ______________________________________                                        1      0.23     7.0     1.61      1.80  1.06                                  2      0.23     7.0     1.61      1.80  1.08                                  3      0.23     7.0     1.61      1.80  1.10                                  4      0.23     7.0     1.61      1.80  1.12                                  5      0.25     8.0     2.00      2.15  1.06                                  6      0.25     8.0     2.00      2.15  1.08                                  7      0.25     8.0     2.00      2.15  1.10                                  8      0.25     8.0     2.00      2.15  1.12                                  9      0.24     10.0    2.40      2.55  1.06                                  10     0.24     10.0    2.40      2.55  1.08                                  11     0.24     10.0    2.40      2.55  1.10                                  12     0.24     10.0    2.40      2.55  1.12                                  13     0.24     11.7    2.81      3.00  1.06                                  14     0.24     11.7    2.81      3.00  1.08                                  15     0.24     11.7    2.81      3.00  1.10                                  16     0.24     11.7    2.81      3.00  1.12                                  ______________________________________                                    

In FIG. 28, triangles represent samples that exhibited color changesfrom white or a non-color close thereto, to black, blue, yellow-green,and pink while the voltage varied from the off-voltage to the on-voltagewhen the ratio P of the off-voltage to the on-voltage was 1.13 (when theduty ratio was set to 1/64 and the bias ratio to 1/9), and crossesrepresent samples that changed color imperfectly. In addition, hollowcircles represent samples that exhibited color changes from white or anon-color close thereto, to black, blue, yellow-green, and pink whilethe voltage varied from the off-voltage to the on-voltage when the ratioP of the off-voltage to the on-voltage was 1.1 (when the duty ratio wasset to 1/120 and the bias ratio to 1/12), and squares represent samplesthat exhibited color changes from white or a non-color close thereto, toblack, blue, yellow-green, and pink while the voltage varied from theoff-voltage to the on-voltage even though the ratio P of the off-voltageto the on-voltage was 1.07 (when the duty ratio was set to 1/240 and thebias ratio to 1/17).

The above results show that the color tone at zero voltage is white or anon-color close thereto and four color changes to black, blue,yellow-green, and pink occur when a voltage is applied, provided thatthe product Δn·d of the optical anisotropy Δn and the thickness d of thenematic liquid crystal 10, the ratio P of the off-voltage to theon-voltage, and the steepness ratio β of the liquid crystal cell 3satisfy the following relationship: ##EQU8##

This relationship is more restrictive than the range of Equation (3)above; it is necessary that the relationship of Equation (6) besatisfied to implement the color changes from white through to pink.

A time division drive circuit was used to provide a pulse widthmodulation drive in eight steps with the duty ratio set to 1/64 and thebias ratio set to 1/9 for a liquid crystal cell 3 in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.23 and thethickness d was 7 μm, in other words in which Δn·d was 1.61 μm, theretardation R of the retardation film 2 was 1.8 μm, and the steepnessratio β of the liquid crystal cell 3 was 1.06, and the colors obtainedat each of these steps were as shown in FIG. 29. The colors white,black, blue, blue-green, green, yellow-green, yellow, and pink weredisplayed at each of these steps.

EMBODIMENT 9

This embodiment illustrates the relationships between the absorptionaxes of the upper and lower polarizing plates, the slow axis of theoptically anisotropic substance, and the directions of rubbing of theupper and lower planes.

A uniaxially drawn film of PC was used as the retardation film 2 in theconfiguration of FIGS. 1 and 3A.

The twist angle T of the nematic liquid crystal 10 was set to 240°, aliquid crystal cell 3 was used in which the optical anisotropy Δn of thenematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the retardation R of theretardation film was 2 μm. Each of the angle θ1 between the direction A1of the absorption axis (or polarization axis) of the upper polarizingplate 1 and the direction B1 of the slow axis of the retardation film 2,the angle θ2 between the direction B1 of the slow axis of theretardation film 2 and the direction of rubbing C1 of the upper plane,the angle θ3 between the direction of rubbing C2 of the lower plane andthe direction A2 of the absorption axis (polarization axis) of the lowerpolarizing plate 4 were varied.

As a result, it was found that the various colors were displayed clearlywithin a preferable range in which the angle θ1 between the direction A1of the absorption axis (or polarization axis) of the upper polarizingplate 1 and the direction B1 of the slow axis of the retardation film 2was 15° to 75°, particularly within the range of 20° to 50°, but thecolor purity dropped dramatically outside this range. In addition, thevarious colors were displayed clearly within a preferable range in whichthe angle θ2 between the direction B1 of the slow axis of theretardation film 2 and the direction of rubbing C1 of the upper planewas 60° to 120°, particularly within the range of 75° to 105°, but thecolor purity dropped dramatically outside this range. Furthermore, thevarious colors were displayed clearly within a preferable range in whichthe angle θ3 between the direction of rubbing C2 of the lower plane andthe direction A2 of the absorption axis (or polarization axis) of thelower polarizing plate 4 was 15° to 75°, particularly within the rangeof 30° to 60°, but the color purity dropped dramatically outside thisrange.

A uniaxially drawn film of PC was also used as the retardation film 2 inthe configuration of FIGS. 1 and 3B.

The various colors were displayed clearly within ranges similar to thosedescribed above, when the twist angle T of the nematic liquid crystal 10was set to 240°, a liquid crystal cell 3 was used in which the opticalanisotropy Δn of the nematic liquid crystal 10 was 0.23 and thethickness d was 7 μm, in other words in which Δn·d was 1.61 μm, and theretardation R of the retardation film was 1.8 μm, but the color puritydropped dramatically outside this range.

EMBODIMENT 10

This embodiment gives examples of the analysis of the effects of twistangle on the nematic liquid crystal.

A uniaxially drawn film of PC was used as the retardation film 2 in theconfiguration of FIGS. 1 and 3A.

A liquid crystal cell 3 was used in which the optical anisotropy Δn ofthe nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the retardation R of theretardation film 2 was 2 μm. Furthermore, the angle θ1 between thedirection A1 of the absorption axis (or polarization axis) of the upperpolarizing plate 1 and the direction B1 of the slow axis of theretardation film 2 and the angle θ3 between the direction of rubbing C2of the lower plane and the direction A2 of the absorption axis (orpolarization axis) of the lower polarizing plate 4 were both set to 35°to 55°, and the angle θ2 between the direction B1 of the slow axis ofthe retardation film 2 and the direction of rubbing C1 of the upperplane was set to 80° to 100°. The color changes that appeared when avoltage was applied were substantially similar to those shown in FIG. 4,as the twist angle T of the nematic liquid crystal 10 was varied withinthe range of 180° to 360° at 20° intervals.

A uniaxially drawn film of PC was also used as the retardation film 2 inthe configuration of FIGS. 1 and 3B. In addition, a liquid crystal cell3 was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the retardation film 2was 1.8 μm. Furthermore, the angle θ1 between the direction A1 of theabsorption axis (or polarization axis) of the upper polarizing plate 1and the direction B1 of the slow axis of the retardation film 2 and theangle θ3 between the direction of rubbing C2 of the lower plane and thedirection A2 of the absorption axis (or polarization axis) of the lowerpolarizing plate 4 were both set to 35° to 55°, and the angle θ2 betweenthe direction B1 of the slow axis of the retardation film 2 and thedirection of rubbing C1 of the upper plane was set to 80° to 100°.

The color changes that appeared when a voltage was applied weresubstantially similar to those shown in the curve (a) of FIG. 7, as thetwist angle T of the nematic liquid crystal 10 was varied within therange of 180° to 360° at 20° intervals.

Although uniaxially drawn films of PC were used as the retardation film2 in Embodiments 2 to 4, and Embodiments 8 to 10, the present inventionshould not be taken as being limited thereto; similar results can beobtained by using retardation films of other materials such as PVA orPSF. Similarly, although the twist angle T of the nematic liquid crystal10 was set to 240° in Embodiments 1 to 9, similar results can beobtained when it is within the range of 180° to 360°. In addition,although the twist angle T of the nematic liquid crystal 10 was measuredcounterclockwise from the direction of rubbing C1 of the upper plane tothe direction of rubbing C2 of the lower plane in Embodiments 1 to 10,similar results can be obtained with a clockwise twist. In such a case,all of the other angles θ1 to θ6 would be measured in the oppositedirection. Furthermore, similar results can be obtained when the productΔn·d of the optical anisotropy Δn and the thickness d of the nematicliquid crystal 10 is greater than 1 μm, provided that the retardation Rof the retardation film 2 satisfies the predetermined relationship.Particularly when a time division drive circuit is used as the drivecircuit 15, Δn·d is preferably at least 1.3 μm in order to obtain clearcolor changes, more preferably at least 1.5 μm. In addition, there is anupper limit of approximately 0.3 to the optical anisotropy Δn of thenematic liquid crystal 10 in practice so that it would be necessary toincrease the cell thickness d in order to increase Δn·d, but in practiceΔn·d is preferably 2 μm or less from consideration of the fact that theresponse speed of the nematic liquid crystal 10 when the off-voltage hasswitched to the on-voltage is proportional to the square of the cellthickness d. In practice, the optical anisotropy Δn of the nematicliquid crystal 10 is preferably within the range of 0.15 to 0.29.

EMBODIMENT 11

This embodiment gives an example of the use of a color polarizing plate.

A uniaxially drawn film of PC was used as the retardation film 2 in theconfiguration of FIGS. 1 and 3B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, and the angle θ2 between the direction B1of the slow axis of the retardation film 2 and the direction of rubbingC1 of the upper plane was set to 80° to 100°. A liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the retardation film 2was 1.6 μm.

In this case, when neutral polarizing plates (NPF-F1220DU, made by NittoDenko) were used as the upper and lower polarizing plates 1 and 4, thecolor tone at zero voltage was a yellowish white and color changes toblack, blue, yellow-green, and pink occurred when a voltage was applied.On the other hand, when blue polarizing plates (B-18245T, made byPolartechno) were used as the upper and lower polarizing plates 1 and 4,the color tone at zero voltage became whiter and the blue that occurredwhen a voltage was applied became bluer.

In a similar manner, when red, blue, or green color polarizing plateswere used as the upper and lower polarizing plates 1 and 4, the purityof that particular color tone increased and the color tone at zerovoltage became closer to white.

EMBODIMENT 12

This embodiment gives an example of varying the thicknesses of the upperand lower substrates.

A uniaxially drawn film of PC was used as the retardation film 2 in theconfiguration of FIGS. 1 and 3B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, and the angle θ2 between the direction B1of the slow axis of the retardation film 2 and the direction of rubbingC1 of the upper plane was set to 80° to 100°. A liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.23 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.61 μm, and the retardation R of the retardation film 2was 1.8 μm.

In this case, when glass substrates of a thickness of 0.7 mm were usedas the upper and lower substrates 7 and 9, the color tone displayed atzero voltage was white and color changes to black, blue, yellow-green,and pink occurred when a voltage was applied; however, when both blackof a low reflection luminance and yellow of a high reflection luminancewere displayed at the same time, parallax between the colors was largebecause yellow-green appeared to be displayed at the position of thereflective plate 5 because the depressions in the front surface of thereflective plate become visible, whereas black appeared to be displayedat the position of the upper polarizing plate 1. On the other hand, whenglass substrates of a thickness of 0.4 mm were used as the upper andlower substrates 7 and 9, this parallax was less than that with 0.7-mmthick glass substrates. Furthermore, when a flexible film such asplastic film was used, this parallax was virtually indistinguishable.

Each of the liquid crystal devices of the above described Embodiments 1to 12 can be made to display more colors than the display colorsdescribed above, by dividing each pixel into a plurality of parts fordriving, and using additive color mixing. Furthermore, each of theliquid crystal devices of Embodiments 1 to 12 may be capable ofdisplaying more colors than those described above, by superimposing twoor more liquid crystal devices. In addition, reflective-type liquidcrystal devices were used by way of example in the above describedEmbodiments 1 to 12, but similar results were obtained withtransflective-type liquid crystal device and even transmittance-typeliquid crystal devices.

In the above description of the embodiments, a time division drivecircuit was used as the drive circuit, but an active matrix drivecircuit such as thin film transistors (TFTs) or metal insulator metal(MIM) could equally well be used.

EMBODIMENT 13

The electronic equipment of this embodiment is a pager in which thereflective type of liquid crystal device of FIGS. 23 and 24B isinstalled.

This pager comprises a pager unit 200, a liquid crystal display 210, anda button 220 for switching operating modes, as shown in FIG. 32.

The liquid crystal display 210 is configured to use the liquid crystaldevice of FIGS. 23 and 24B.

In this embodiment, the twist angle T1 of the nematic liquid crystal 10filling the liquid crystal cell 3 of FIG. 23 was set to 240° and thetwist angle T2 of the nematic liquid crystal 10 filling the secondliquid crystal cell 26 was also set to 240°.

In addition, the angle θ1 between the direction A1 of the absorptionaxis (or polarization axis) of the upper polarizing plate 1 and thedirection of rubbing B1 of the upper plane of the second liquid crystalcell 26 and the angle θ3 between the direction of rubbing C2 of thelower plane of the liquid crystal cell 3 and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, and the angle θ2 between the direction ofrubbing B2 of the lower plane of the second liquid crystal cell 26 andthe direction of rubbing C1 of the upper plane of the liquid crystalcell 3 was set to 80° to 100°.

The optical anisotropy Δn of the nematic liquid crystal 10 filling theliquid crystal cell 3 was 0.23 and the thickness d thereof was 7 μm, inother words Δn·d was 1.61 μm, and the optical anisotropy Δn of thenematic liquid crystal 10 filling the liquid crystal cell 26 was 0.23and the thickness d thereof was 7 μm, in other words Δn·d was 1.61 μm.The same liquid crystal filled both the liquid crystal cell 3 and thesecond liquid crystal cell 26.

The liquid crystal device installed in this pager was set in such amanner that the color tone of the background color display was white ata tone level 0 (at the off-voltage), the display of ordinaryalphanumeric characters was black at a tone level 3, and the display ofemphasis or warning messages was yellow-green at a tone level 5 or pinkat a tone level 7 (at the on-voltage).

This pager was not only capable of displaying more information at a highreflection luminance and with improved visibility of the color display,the use of a reflective device enabled a sufficiently low powerconsumption.

In addition, since the same liquid crystal was used as the nematicliquid crystal 10 that filled the liquid crystal cell 3 and the nematicliquid crystal 10 that filled the second liquid crystal cell 26, theratio of the respective nematic-isotropic phase transition temperatures(clearing point or NI point) was 1 and thus the various colors could beperceived over a temperature range of -20° C. to 70° C.

Note that the liquid crystal cell 3 was driven by the drive circuitryshown in FIG. 33. This display circuitry comprises a calculation section500, a key input section 510, a color control section 520, and a drivecircuit 530. The calculation section 500 comprises a CPU 300, a memorycircuit 310, a calculation circuit 320, and a display signal generationcircuit 330. The CPU 300 controls the operations of all of thecircuitry.

The key input section 510 is provided with input keys 340, and theconfiguration is such that signals that are input by using these inputkeys 340 are transferred to the CPU 300.

The color control section 520 is provided with a color selection signalgeneration circuit 35°.

The drive circuit 530 is provided with a drive waveform shaper circuit360, a drive voltage selection circuit 370, and a drive voltagegeneration circuit 380. The drive voltage generation circuit 380 causesvoltages of different voltage levels to be generated. The drive voltageselection circuit 370 selects a voltage level in answer to aninstruction from the color selection signal generation circuit 35° ,then supplies it to the drive waveform shaper circuit 360. The drivewaveform shaper circuit 360 creates a drive waveform for the liquidcrystal cell 3 on the basis of the voltage supplied from the drivevoltage selection circuit 370 and a display signal supplied from thedisplay signal generation circuit 330, and the liquid crystal cell 3 isdriven by this drive waveform.

EMBODIMENT 14

The electronic equipment of this embodiment is an electronic organizerin which a liquid crystal display is installed.

In this embodiment, the liquid crystal display is configured of theliquid crystal device shown in FIGS. 1 and 3B.

In the configuration of FIGS. 1 and 3B, a uniaxially drawn film of PCwas used as the retardation film 2. In addition, the twist angle T ofthe nematic liquid crystal 10 was set to 240°, the angle θ1 between thedirection A1 of the absorption axis (or polarization axis) of the upperpolarizing plate 1 and the direction B1 of the slow axis of theretardation film 2 and the angle θ3 between the direction of rubbing C2of the lower plane and the direction A2 of the absorption axis (orpolarization axis) of the lower polarizing plate 4 were both set to 35°to 55°, and the angle θ2 between the direction B1 of the slow axis ofthe retardation film 2 and the direction of rubbing C1 of the upperplane was set to 80° to 100°.

A liquid crystal cell 3 was used in which the optical anisotropy Δn ofthe nematic liquid crystal 10 was 0.23 and the thickness d was 7 μm, inother words in which Δn·d was 1.61 μm, and the retardation R of theretardation film 2 was 1.8 μm. This reflective type of liquid crystaldevice was installed in the electronic organizer.

In this example, a graphics display controller (SED1351F, made by SeikoEpson Co.) was used as the drive circuit 15.

This graphics display controller is capable of selecting the display oftwo intermediate tones from eight steps between an off-voltage and anon-voltage, in addition to the off-voltage and on-voltage. From thesesteps, the display was set in such a manner that the color tone of thebackground color display was white at a tone level 0 (at theoff-voltage), the display of ordinary alphanumeric characters was blackat a tone level 3, and the display of emphasis or warning messages wasyellow-green at a tone level 5 or pink at a tone level 7 (at theon-voltage). In this example, the frame frequency is preferably either70 to 110 Hz or 120 to 180, because flickering that disrupts the screenis generated at other frequencies.

This electronic organizer was not only capable of displaying moreinformation at a high reflection luminance and with improved visibilityof the color display, the use of a reflective device enabled asufficiently low power consumption.

EMBODIMENT 15

The electronic equipment of this embodiment is a personal digitalassistant (PDA) in which a liquid crystal display is installed.

In this embodiment, a uniaxially drawn film of PC was used as theretardation film 2 in the configuration of FIGS. 1 and 3B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, theangle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were both set to 35° to 55°, and the angle θ2 between the direction B1of the slow axis of the retardation film 2 and the direction of rubbingC1 of the upper plane was set to 80° to 100°. A liquid crystal cell 3was used in which the optical anisotropy Δn of the nematic liquidcrystal 10 was 0.22 and the thickness d was 7 μm, in other words inwhich Δn·d was 1.54 μm, and the retardation R of the retardation film 2was 1.7 μm.

The above reflective type of liquid crystal device was installed in thePDA. In this example, a graphics display controller (SED1351F, made bySeiko Epson Co.) was used as the drive circuit. In addition,touch-sensitive keys were super imposed on the upper polarizing plate 1to act as an input device.

The configuration was such that a palette of selectable tone levels wasdisplayed on the screen, so that, if a palette corresponding to eachtone level is selected by a pen-input device, alphanumeric characterscan be displayed in a color corresponding to the voltage of the tonelevel selected. This enables the creation of an inherently colorfulscreen display, so that more information can be displayed in aneasy-to-read fashion.

Therefore, the liquid crystal device of this invention could beinstalled in a more advanced personal portable information apparatus1000, as shown in FIG. 36. The personal portable information apparatus1000 of FIG. 36 comprises an IC card 1100, a simultaneous interpretationsystem 1200, a handwriting input screen 1300, a TV conferencing system1400a and 1400b, a map information system 1500, and a liquid crystaldisplay screen 1660.

The personal portable information apparatus 1000 is also provided with avideo camera 1610, a speaker 1620, microphone 1630, an input pen 1640,and earphones 1650 in an input-output interface unit 1600.

EMBODIMENT 16

The electronic equipment of this embodiment is a calculator or acontroller for an air-conditioner in which a liquid crystal display isinstalled.

In this embodiment, a uniaxially drawn film of PC was used as theretardation film 2 in the configuration of FIGS. 1 and 3B.

The twist angle T of the nematic liquid crystal 10 was set to 240°, boththe angle θ1 between the direction A1 of the absorption axis (orpolarization axis) of the upper polarizing plate 1 and the direction B1of the slow axis of the retardation film 2 and the angle θ3 between thedirection of rubbing C2 of the lower plane and the direction A2 of theabsorption axis (or polarization axis) of the lower polarizing plate 4were set to 35° to 55°, and the angle θ2 between the direction B1 of theslow axis of the retardation film 2 and the direction of rubbing C1 ofthe upper plane was set to 80° to 100°.

A liquid crystal cell 3 was used in which the optical anisotropy Δn ofthe nematic liquid crystal 10 was 0.22 and the thickness d was 7 μm, inother words in which Δn·d was 1.54 μm, and the retardation R of theretardation film 2 was 1.7 μm.

The above described reflective type of liquid crystal device wasinstalled as a display device in a controller of an air-conditioner. Theexternal appearance of this air-conditioner controller is shown in FIG.34A. This controller 610 is provided with a liquid crystal display 620and input keys 630 and is designed to provide remote control over anair-conditioner 600.

A time division drive circuit that varies an on-voltage by varying abias ratio was used as the drive circuit. In other words, the liquidcrystal device was set in such a manner that a background color of whiteand another single color can be displayed simultaneously.

The configuration is such that alphanumeric characters are displayed inblue when the air-conditioner is functioning as a cooler, and in orangewhen it is functioning as a heater. In this manner, the configuration ofthe drive circuitry can be made comparatively simple by causing thevoltage to vary over the entire screen surface, and thus an inexpensivedrive system can be used.

Note that the liquid crystal display 620 installed in theair-conditioner controller of FIG. 34A is configured to be driven by thecircuitry shown in FIG. 35.

The circuitry shown in FIG. 35 comprises a calculation section 502, akey input section 512, a color control section 522, and a drive circuit532.

The calculation section 502 comprises a CPU 302, a memory circuit 312, acalculation circuit 322, and a display signal generation circuit 332.The CPU 302 controls the operations of all of the circuitry.

The key input section 512 is provided with input keys 342, and theconfiguration is such that signals that are input by using these inputkeys 342 are transferred to the CPU 302.

The color control section 522 is provided with a color selection signalgeneration circuit 352.

The drive circuit 532 is provided with a drive waveform shaper circuit362 and a drive voltage generation circuit 382. The drive voltagegeneration circuit 382 selects bias ratios in answer to instructionsfrom the color selection signal generation circuit 352, causes voltagesof different voltage levels to be generated, and supplies them to thedrive waveform shaper circuit 362.

The drive waveform shaper circuit 362 creates a drive waveform on thebasis of the voltage supplied from the drive voltage generation circuit382 and a display signal supplied from the display signal generationcircuit 332, then drives the liquid crystal display 620 with thiswaveform.

The liquid crystal device of this invention can also be installed in asmall calculator as shown in FIG. 34B, in a similar manner to the aboveexamples of electronic equipment. It can also be used as a displaydevice in a games machine or any type of audio equipment in which acolor display is necessary. The use of the liquid crystal device of thisinvention makes it possible to provide electronic equipment that isbright, easy to see, informative, and with a low power consumption.

We claim:
 1. A liquid crystal device comprising a liquid crystal cell having a layer of nematic liquid crystal twisted to within the range of 180° to 360° and a pair of substrates on which are formed electrodes for applying a voltage to said nematic liquid crystal layer and which are disposed in an opposing manner in a form that sandwiches said nematic liquid crystal layer therebetween;a pair of polarizing plates disposed on either side of said liquid crystal cell in a sandwich form; a retardation film formed of polyvinyl alcohol (PVA) and provided between said liquid crystal cell and at least one polarizing plate of said pair of polarizing plates; and voltage application means capable of selecting at least three voltages to be applied between said pair of substrates; wherein: said liquid crystal cell and said retardation film satisfy the relationships of Equations 1 and 2 below:

    Δn·d≧1(μm)                        Equation 1

    0.51≦R-Δn·d≦1.21(μm)       Equation 2

where: Δn·d is the product of the optical anisotropy Δn of said nematic liquid crystal layer and the thickness d of said nematic liquid crystal layer; and R is the sum of the products Δnj·dj of the optical anisotropy Δnj of a jth (where j is an integer) layer of said retardation film and the thickness dj of the jth layer of said retardation film, taken from a first layer to an ith layer (where i is an integer greater than or equal to j) when i layers of said retardation film are used.
 2. Electronic equipment in which is installed a liquid crystal device as defined in claim
 1. 3. Electronic equipment in which is installed a liquid crystal device as defined in claim 1, and which is also provided with an input means for inputting data necessary for displaying an image on said liquid crystal device.
 4. A liquid crystal device comprising a liquid crystal cell having a layer of nematic liquid crystal twisted to within the range of 180° to 360° and a pair of substrates on which are formed electrodes for applying a voltage to said nematic liquid crystal layer and which are disposed in an opposing manner in a form that sandwiches said nematic liquid crystal layer therebetween;a pair of polarizing plates disposed on either side of said liquid crystal cell in a sandwich form; an optically anisotropic substance provided between said liquid crystal cell and at least one polarizing plate of said pair of polarizing plates; and voltage application means capable of selecting at least three voltages to be applied between said pair of substrates; wherein: said liquid crystal cell and said optically anisotropic substance satisfy the relationships of Equations 7 and 8 below:

    Δn·d≧1(μm)                        Equation 7

    15.5×α.sup.2 -40×α+25.1≦R-Δn·d≦15.5×.DELTA..sup.2 -40×α+25.8(μm)                    Equation 8

where: Δn·d is the product of the optical anisotropy Δn of said nematic liquid crystal layer and the thickness d of said nematic liquid crystal layer; R is the sum of the products Δnj·dj of the optical anisotropy Δnj of a jth (where j is an integer) layer of said optically anisotropic substance and the thickness dj of the jth layer of said optically anisotropic substance, taken from a first layer to an ith layer (where i is an integer greater than or equal to j) when i layers of said optically anisotropic substance are used; and a is the ratio of the optical anisotropy of said optically anisotropic substance at a wavelength of 450 nm with respect to the optical anisotropy of said optically anisotropic substance at a wavelength of 590 nm.
 5. The liquid crystal device of claim 4, wherein:said means capable of selecting at least three values of voltage to be applied between said pair of substrates is a time division drive circuit that is capable of applying at least one other voltage between a selected voltage and a non-selected voltage, in addition to said selected voltage and said non-selected voltage.
 6. The liquid crystal device of claim 5, wherein:said optically anisotropic substance is a second liquid crystal cell having an orientated liquid crystal filling a space between said pair of opposed substrates.
 7. The liquid crystal device of claim 4, wherein:said liquid crystal cell satisfies the relationship of Equation 9 below: ##EQU9## where Δn·d is the product of the optical anisotropy Δn of said nematic liquid crystal layer and the thickness d of said nematic liquid crystal layer; β is the ratio of the voltage at which the capacitance of said liquid crystal cell is 0.3 to the voltage at which the capacitance of said liquid crystal cell is 0.1, when the capacitance of said liquid crystal cell is 0 for a voltage of 0.5 V applied between said pair of substrates and the capacitance of said liquid crystal cell is 1 for a voltage of 25 V applied between said pair of substrates; and P is the ratio of a selected voltage to a non-selected voltage.
 8. The liquid crystal device of claim 7, wherein:said optically anisotropic substance is a second liquid crystal cell having an orientated liquid crystal filling a space between said pair of opposed substrates.
 9. The liquid crystal device of claim 4, wherein:said optically anisotropic substance is a polymer film.
 10. The liquid crystal device of claim 9, wherein:said polymer film that is said optically anisotropic substance has a refractive index nx in the direction of the maximum refractive index parallel to the film surface, a refractive index ny in a direction perpendicular to nx and parallel to the film surface, and a refractive index nz in the film thickness direction, where said refractive indices satisfy the relationship of Equation 10 below:

    (nx-nz)/(nx-ny)≦0.7                                 Equation
 10.


11. The liquid crystal device of claim 9, wherein:the direction of the slow axis of said polymer film that is said optically anisotropic substance is parallel to the film surface and also varies continuously with respect to said film thickness direction.
 12. The liquid crystal device of claim 4, wherein:said optically anisotropic substance is a second liquid crystal cell having an orientated liquid crystal filling a space between said pair of opposed substrates.
 13. The liquid crystal device of claim 12, wherein:the liquid crystal used in said second liquid crystal cell is a nematic liquid crystal, and the ratio of the nematic first-order phase transition temperatures of said nematic liquid crystal in said second liquid crystal cell and said nematic liquid crystal used in another liquid crystal cell is in the range of 0.8 to 1.2.
 14. The liquid crystal device of claim 4, wherein:at a contacting surface between one polarizing plate of said pair of polarizing plates and said liquid crystal cell, the angle between the direction in which molecules of said nematic liquid crystal are aligned in contact with the inner surface of said liquid crystal cell and one of the absorption axis and polarization axis of said polarizing plate is within the range of 15° to 75°.
 15. The liquid crystal device of claim 4, wherein:at a contacting surface between said liquid crystal cell and said optically anisotropic substance, the angle between the direction in which molecules of said nematic liquid crystal are aligned in contact with the inner surface of said liquid crystal cell and the slow axis of said optically anisotropic substance is in the range of 60° to 120°.
 16. The liquid crystal device of claim 4, wherein:at a contacting surface between said optically anisotropic substance and one polarizing plate of said pair of polarizing plates, the angle between the slow axis of said optically anisotropic substance and one of the absorption axis and polarization axis of said polarizing plate is in the range of 15° to 75°.
 17. The liquid crystal device of claim 4, wherein:one of a reflective plate and transflector is further provided on an outer side of one polarizing plate of said pair of polarizing plates.
 18. A liquid crystal device comprising a liquid crystal cell having a layer of nematic liquid crystal twisted to within the range of 180° to 360° and a pair of substrates on which are formed electrodes for applying a voltage to said nematic liquid crystal layer and which are disposed in an opposing manner in a form that sandwiches said nematic liquid crystal layer therebetween;a pair of polarizing plates disposed on either side of said liquid crystal cell in a sandwich form; a retardation film formed of polycarbonate (PC) and provided between said liquid crystal cell and at least one polarizing plate of said pair of polarizing plates; and voltage application means capable of selecting at least three voltages to be applied between said pair of substrates; wherein: said liquid crystal cell and said retardation film satisfy the relationships of Equations 3 and 4 below:

    Δn·d≧1(μm)                        Equation 3

    -0.08≦R-Δn·d≦0.62(μm)      Equation 4

where: Δn·d is the product of the optical anisotropy Δn of said nematic liquid crystal layer and the thickness d of said nematic liquid crystal layer; and R is the sum of the products Δnj·dj of the optical anisotropy Δnj of a jth (where j is an integer) layer of said retardation film and the thickness dj of the jth layer of said retardation film, taken from a first layer to an ith layer (where i is an integer greater than or equal to j) when i layers of said retardation film are used.
 19. A liquid crystal device comprising a liquid crystal cell having a layer of nematic liquid crystal twisted to within the range of 180° to 360° and a pair of substrates on which are formed electrodes for applying a voltage to said nematic liquid crystal layer and which are disposed in an opposing manner in a form that sandwiches said nematic liquid crystal layer therebetween;a pair of polarizing plates disposed on either side of said liquid crystal cell in a sandwich form; a retardation film formed of polysulfone (PSF) and provided between said liquid crystal cell and at least one polarizing plate of said pair of polarizing plates; and voltage application means capable of selecting at least three voltages to be applied between said pair of substrates; wherein: said liquid crystal cell and said retardation film satisfy the relationships of Equations 5 and 6 below:

    Δn·d≧1 (μm)                       Equation 6

    -0.40≦R-Δn·d≦0.30(μm)

where: Δn·d is the product of the optical anisotropy Δn of said nematic liquid crystal layer and the thickness d of said nematic liquid crystal layer; and R is the sum of the products Δnj·dj of the optical anisotropy Δnj of a jth (where j is an integer) layer of said retardation film and the thickness dj of the jth layer of said retardation film, taken from a first layer to an ith layer (where i is an integer greater than or equal to j) when i layers of said retardation film are used. 